Just make sure that you get a decent amount of memory, and a fairly big harddrive. Most new PC's will be packaged with VISTA which is a dog unless you got a load of memory. 300GB plus hard drive would be good but you will probably eat that up once you get into it and start loading up all your music, ripping your dvd's, porn, games etc etc.
Make sure it has a DVD burner, front USB ports (having to pull the box out from under your desk everytime you need to plug in your USB stick is a pain). It will have an inbuilt network card so make sure you have an RJ45 ethernet cable, you probably do, check the box that your ADSL router came in. Probably has wireless too!!!
DELL and HP do some fairly ok compact machines, I robbed errrrrr, borrowed a GX620 from work, slapped 4gb memory in it and upgraded the hard drive to a 750GB SATA drive (make sure you get a SATA drive, which it probably will have anyway, much faster than IDE drives) and it works like a dream.
Go for a 17 or a 19 inch monitor. Make sure it has a decent graphics card, ATI with 512MB does the job.
As for the processor, it's all Pentium dual core blah di blah jow days, so dont worry, some people go for AMD some go for INTEL, unless you are really into gaming etc you wouldnt notice the difference, operate on the "the higher the number the better it must be" way of thinking

. You could go down the 64bit route but I think that would just complicate the issue for you. You wont notice any difference, it will be quick.
Use AVG for antivirus, it's free and came be downloaded. I assume you have OFFICE, check to see if it is including in the bundle when you buy the machine as the new version (Office 2007) is expensive on it's own, but there are plenty of people who have hooky copies.
You could buy a Mac, great machines but expensive and there is not as much software available (Im talking about dodgy copies of programs that all your mates have for PC). This in my opinion why PCs are better than Macs for home users, plain and simple, more software (that you would probably never use anyway). Mac is the overall better machine and OS before anyone of the Mac lot start screaming at me.
But than again I use Slackware which pisses over all of you, Microsoft and Mac put together

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In short, processor, memory, disk space, burner... for 750 you will get a decent machine for home use that you wont have to upgarde for a good while and will get the job done.
Hope this helps

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