Since that's a lot of ground to cover, I'll give you the recommended and maximum specs available on the PocketPC, as well some info on the top PDAs available.
Recommended Minimums:
Processor: 400MHz XScale
RAM: 64 MB
ROM: 64 MB
Wireless: Bluetooth
Screen: 3.5'' QVGA 240x320 Display
Battery: Rechargable
Memory Card: SecureDigital(SD)
Maximum Available:
Processor: 624MHz XScale
RAM: 128 MB
ROM: 128 MB (A few have up to 256MB)
Wireless: Bluetooth + WiFi
Screen: 3.7'' VGA 480x640 Display
Battery: Removable and Rechargable
Memory Card: SecureDigital(SD) and CompactFlash(CF)
For more information, check out the Cnet Handheld Buyer's Guide. (Note that it is a few months old, so not all of the recommended specs are accurate. However, it still provides a lot of useful information.)
RAM is used like RAM on the computer, as well as for storage purposes. ROM is used to store the OS and for storage (with WindowsMobile taking around 32MB). Bluetooth lets you communicate wirelessly with bluetooth-enabled cell phones, computers, printers, keyboards, headsets, and GPS devices. However, it is rather slow. WiFi will let you connect to the internet where ever a ''hotspot'' is available, as well as to your WiFi-enabled computer.
The VGA screen provides for a much higher level of clarity, but it will cost you...both money and battery power. The more powerful the processor, the more games and movies you can handle, as well as multitasking. Some of the current applications require a 400MHz processor, and anything less is quickly becoming obsolete. RAM also facters into this.
HP is currently the leading manufacturer, but tend to be greatly overpriced. Thus, I recommend a Dell Axim. Dell currently has 2 lines available...the X30 line is about a year old and will be ''retired'' soon, but the X30 High still one of the most powerful PDAs available. The X50 is over 6 months old and boasts pretty much the same specs as the X30, but cost $100 more. You can see all the HP PDAs here, and compare the Dells here. Yu can also check out Dave's PDA Place to get data on all PocketPCs currently available. Once you have chosen a few models, be sure to check them out on Cnet Handheld Reviews.
Also to note: The next version of WindowsMobile will be out shortly, which will offer ''persistent memory,'' advanced Office features, and more. (Check it out here.) This update will olny be available on select PDAs (Including the Axim X50 and some HP Ipaqs, but not the X30), and will cost $30-$50 if your PDA does not come with it preinstalled.
As far as applications, there are thousands! It ranges from customized versions of MS Office and Money to games like the original Doom. Plus there is an unlimited database of programs designed specifically for the PocketPC. You can check out the popular sites, such as Handango, Handmark, Astraware, and FreewarePPC. In addition, there are sites dedicated to specific handhelds, such as AximSite and IPaqHQ.
Hope this helps,
John