I used to be an IT manager for a large telecom/interconnect company - I was responsible for about 500 PCs and 500 Macs, all the interconnectivity between 13 offices, remote access, networks security, shared resources (file servers, printers, etc), LAN, WAN throughout California... so... now that my background is out of the way, let's tackle your questions one at a time:
1- is it true that this computer does not crash ,gets viruses or spywares etc..... ?
Sort of. Any computer will crash. Crashes happen for different reasons. Hard drive failure can cause a computer to crash. So can complex code that causes conflicts with other code on the machine. My 17 inch iMac flat panel has never crashed. I have been running an application that unexpectedly quit, but since MacOSX is running on top of a multi-threaded Unix environment, the entire machine didn't throw up. I know people who have had their Macs lock up and cause problems. I know a whole lot more Windows users whose machines have locked up (when one application dies. The "blue screen of death" happens way too often - even in my Windows XP Dell machine.
On viruses: That could take days - but how about this: I don't have an antivirus application on my iMac Flatpanel G5. The bulk of the viruses that can infect a Mac come from MS Office (Excel, PowerPoint, Word). I use NeoOffice which provides equivalent capabilities but does not get infected by the MS-Office suite. Some will say thet there are no viruses for Macs because they are such a small target. I'm cool with that. Other will say that because of the operating system environment, it is much more difficult to write and spread Mac-specific viruses. I'm cool with that, too. Lots of the spyware out there is written for specific applications and needs to reside in specific directories... typically MS Internet Explorer. Great. I use Safari (bundled with the machine) and FireFox. And if the web-site coder is too lazy to be sure their code works cross-platform, then that site does not deserve my business. Too many security issues with MS Internet Explorer.
So, the short answers you your question #1: No; Yes; Yes.
2- if yes ,why people buy widows based pcs besides the costs ?
It depends what you want to do with the computer. It used to be that there were 40,000 applications for DOS and Windows and 15,000 applications for Macintosh. Count the applications you are likely to use:
Word Processing, Spreadsheet, Presentation, Image manipulation, Video editing, audio editing, audio library, Browser, email... you think of some... anyway, just for laughs, lets triple the number... so let's say 30... or 40... this does not approach a requirement to have to wade through 10,000 let alone 15,000 or 40,000 or more. Lot's of people convinced themselves that getting in cheap with a PC was the way to go. There have been recent real-life comparisons of similarly equipped Macs compared to Dell machines. And Dll's are supposed to be "affordable"... but when similarly equipped, the Apple machines were less expensive.
In my experience, over a 5 year period, Windows computers are more expensive than Apple Macintosh computers - presuming they have similar capabilities at the start. In addition to the hardware expense, one needs to consider the support expense as well.
3- can I run msn messenger ,yahoo messenger or skype on it ?
MSN Messenger: Don't know, don't care.
Yahoo messenger: Yes. (I use it through the included iChat application)
Skype: http://www.skype.com/download/skype/macosx/
4- If I buy the imca 20 " what kind of problems I could face ?( please note that I don't want to run windows on it )
As I said at the beginning of this post, I used to be an IT manager. My house if full of Apple gear because the last thing I wanted to do was come home and troubleshoot machines for my wife and son. When I was an IT manager, I would get about 1 Mac problem call for every 6-7 Windows problem calls (remember, I had 500 of each). My house is networked (10/100BaseT) using CAT5 cable and a Belkin wireless router connected to DSL. There is a six year old HP5000N laser printer on the network. There is a USB-connected Canon MP780 shared by a G4 tower and a G5 flatpanel iMac. And when I bring my Dell laptop home and my son brings his PowerBook home (he's in college, now), everyone and everything shares the network - wired and wirelessly.
Since you don't want to run Windows on it, you just eliminated 70% of your potential problems (i.e., viruses, hackers, spyware, etc...).
The problems you can expect are not limited to Apple machines, but similar to any piece of high-end electronics. Use the knowledge-base at Apple.com. Find out if there is a Macintosh User Group near where you live (search Apple.com).
Let your son know that Worlds of Warcraft, StarCraft and other massive online games are available for MacOSX - and they work GREAT.
5- do you guys advice me to buy it now ,or wait until the new OS comes out ?
Waiting for the next cool thing whether Windows Vista, Macintosh OSX, camcorders, cars, whatever, means you were not able to use the machine for that period of time until you finally decided to get it. I don't work for Apple or any compnay that is affiliated with Apple. I would recommend getting the machine at anytime - and now is as good of a time as any... In addition to the machine I would recommend that you get an external drive for backing up the data on the computer and I would increase the RAM on the machine -- so likely 2 gig of RAM minimum. And invest in a good surge suppresor - not a cheap $15 one... but a good one... say, $45 or so. I would give these same recommendations for ANY new computer purchase... Macintosh or otherwise.
I don't know how old your son is. Mine's 19 - and he's had his own computer since he was about 5. He now has a 17" Core Duo flat panel iMac and a PowerBook 15" G4...
Over the years, I've heard LOTS of people tell me how much they LOVE their Macs... and a few who were indifferent about them... but I have NEVER heard a Windows user say they love their machine - rather (unless they are a power user or hobbyist), they are typically intimidated by their machine.
thank you very much !
Thank YOU very much - sorry for the long post - but there are no short answers to your questions (except for #3)...
Bill