I didn't really know where to put this topic so I bunged it on here. If your getting a new computer ready for Vista and you don't know what to do with your old one I have a suggestion. Reformat it, reload Windows XP, take everything off of it except for your email and web browser programs and then use it for the internet. In that case if you do get a virus or some such nasty you will not run the risk of losing loads of personal data. If you want to download something for your new computer you can save it and transfer it over with a pen drive, or via a network, after virus checking it. Other good thing is that one person can be using the new computer whilst the other is using the old one on the internet.
Better is to do a clean install of Windows on the old one and give it to charity. As Al94 says, with a modicum of care you won't pick up nasties on the internet. I can't remember the last time I had anything worse than cookies show up in my regular scans.
I haven't bought a new computer for just over 8 years. I just take all the parts out and upgrade it over time. At the moment, the only original component in mine is it's case (click here for a pic, at least it's less likely to get nicked). I run AVG and ZoneAlarm and I've never had anything nasty on it or any hacking attempts, but I suppose it's a bit of added security if you use one just for Internet and the other for regular use. It just uses up more power which gives you a bigger electric bill. ;-)
I too upgrade rather than buy a whole new PC and sell the old bits on eBay, so they get reused. The only exception was my first PC, which I replaced with a new system. The old one is still with the friend who bought it off me and, some 5 years later, still in daily use.
Currently have 9 PCs working, (I have trouble throwing anything away ;0) ).
This one, a P4 Medion bought a couple of years ago networked to My old 1.4 Athlon which contains my backups for everything on this one.
IBM think pad for work running XP SP2, HP laptop running 2000, old works one which I use to backup all my work stuff.
Old ATX one running ME Old AT one running 98
old 486 that only has DOS 6 and an old diagnostic program I use for training at work Old 386 laptop (Tempus approx 1992)running DOS 6 for training Old 286 laptop (Tempus approx 1988) running DOS 5, again for training. This "Laptop" is as big as my Medion.
Plus several boxes of spares,. Anyone remember daisywheel printers? :0)
Almost forgot the two ZX Spectrums 48k and 128K they should still work if I get them out of the loft and plug them in.
I wouldn't like your electric bill, but I assume you don't have them all on at the same time. I don't suppose you're part octopus are you. It seems to me that one pair of hands just wouldn't be enough.