Okay, looks like you want an all-around PC then.
OS: Windows XP - Best all-around OS
CPU:Looks like you'd be happy with an Intel Core 2 Duo clocked at 1.2GHz. Best bang for the buck. Some people say AMD is better...well Core 2 Duo and Core 2 Extreme have trounced anything AMD has cooked up.
RAM: 1.5GB is reasonable, but you can get by with 1 GB.
Graphics Card: If you have a PCI slot, get this cheap, powerful card for $20: http://www.newegg.com/Product/Product.aspx?Item=N82E16814102737. Just make sure to get the 1.5 RAM if yyou buy this one, cuz it sucks up RAM.
If you're not custom building, 256MB with a fan is good enough, maybe 512MB if you play games at full settings.
HD: Slack off on this if you've been doing heavy spending. 40GB should be enough, you don't need a fast storage one either.
Monitor: These things are expensive, so get an LCD equal or less than 17." The smaller the size, the better the performance (and the price!). If you do visual things like gaming and graphics-intensive programs, go for a sharper screen, but a basic LCD should be cheap and adequate.
Software: All you really need to start of with are Firefox, Microsoft Office 2004, and Norton Anti-Virus. No biggie.
Hope this helps, and it helps more if you're custom building. This should make a good PC at a reasonable price, especially if you buy from Newegg.com.