I started with a fresh install of Windows XP. It is always a good idea to save your valued files and folders, gather all of your installation discs, and then reformat and reinstall XP. That way you avoid having to trouble shoot for incompatible programs, drivers, etc. Over time you tend to collect "junk" files which seem to be benign but they begin to clutter up the the hard drive and eventually slow things down.
I am extremely suspicious of "name brand" computers because they ALWAYS load crap onto the hard drive as a "service" to you when you buy their product. I also do not like the idea of having proprietary hardware on those "name brand" computers which prevent you from upgrading unless you go back to them! I always build my own "white box", but you can also have any computer store build you one to your specifications for just a little more. I paid around $200 for a motherboard with onboard sound and network card and processor, $100 for memory, $70 for a 128 meg video card. I used my existing dvd burner and hard drive but did upgrade my power supply to a 500 watt because I run a lot of periphrials (scanner, camera,printer, tv card, etc.). So, for around $500 I get exactly what I want and load only those things I want loaded.
The drawback is that there is no warantee or customer support but I am an unredeemable meddler who just can't stop himself from tearing into things to see how they work and how to make them better. I have also successfully infected a number of my aquaintances with this disease and they always call me when they have trouble with their "new and improved" computer.
You also have to reconcile yourself with the fact that you will have to upgrade every couple of years, at least the motherboard and processor. Most people are satisfied to plug along with a box that is three or four years old but software and hardware demands change so quickly that you just can't afford to stand pat for that long. E Machines area good idea for those who only want to go on the internet for email and word processing but that is too limiting for MY taste. Even though I may never get into video editing and advanced graphics design I still want the flexibility of leaving that option open.