Why not get a wireless (WiFi) printer since any printer server will cost just as much. Also, the setup is not the only thing you would learn but when another machine won't print you dive into another deeper pool of issues that you don't seem ready for.
There is no single paragraph I could write to begin to cover it all (unless I wrote to google it?) so the simplest solution is to get a WiFi printer and then let them print to it.
As to sharing files. I can start by using DROPBOX (see google).
In my home we have an iMac G5, two laptops running Windows XP, and one desktop, also XP. We have an O2 wireless box iv (which I believe is a rebadged Thomson SpeedTouch TG587nv2) to which the mac and desktop pc are wired and the two laptops connect wirelessly. One of the laptops is mine, and i would like to be able to connect to the mac to share files etc, and possibly to the other pcs, but this is not imperative. I have a printer connected to the mac, and one to the pc, which I would like to be able to access from any of the laptops. I haven't got a clue how to start setting this up! could anyone offer advice please? can i use the wireless router as a print server? what are the security implications of having all the computers networked i.e if a virus infected one, could it spread through the network? Most of the people in my house are even more clueless than me, I wouldn't want one of them clicking on an email attachment and infecting everyone! thanks in advance for any help and advice.