Let's take price out of the equation. Let's just say that I want to buy an all-around excellent gaming rig without paying extra for one component over another when, in practice, I'm not going to notice the difference anyway. What can I expect to pay if I'm starting from scratch, and what advice would you give in terms of hardware to look out for?
Technology and prices change all the time. Telling you what to look out for or to consider now may become a bad idea many months from now when you finally get the money. The time to ask "what to buy?" is the time when you're actually
ready to buy. So if a new machine is what you want, just focus on saving the money first. About $800 is a good amount to aim for at the very least if you need everything.
Now if you want to make some light upgrades to tie you over with your current system, it can be done to an extent. I took a look at your current system and I see that it is an HP-based one. Baaaaaad idea trying to power the 8800GT with the stock HP power supply. Anyways, the motherboard will take up to an X2 5000+ processor:
http://h10025.www1.hp.com/ewfrf/wc/document?docname=c00757531&tmp_task=prodinfoCategory&lc=en&dlc=en&cc=us&lang=en&product=3339286#N94
These upgrades will get you running pretty well and won't break the bank:
CPU: http://www.superbiiz.com/detail.php?name=ADO-5000DO&title=AMD-Athlon-X2-Dual-Core-Processor-5000-2-6GHz-AM2-OEM
GPU: http://www.newegg.com/Product/Product.aspx?Item=N82E16814102859
PSU: http://www.newegg.com/Product/Product.aspx?Item=N82E16817139004
A lil over $200. The processor is OEM, meaning no heatsink fan. However, the one that is being used for your X2 3800+ should be the same copper pipe version that the X2 5000+ would use...so should be reusable. Will want to look intohttp://www.newegg.com/Product/Product.aspx?Item=N82E16835100007&cm_re=arctic_silver_5-_-35-100-007-_-Productas well to reapply thermal compound. There are excellent instructions on how to apply it all over the internet.
The video card and power supply can be carried over to your new machine later on should you decide to do the major overhaul. I realize there are cards like the Radeon 6850 and 6870 or the GeForce 460 out right now, but the Radeon 5750 is about the most I'd go with a X2 5000+. Up to you if want to tolerate more of a bottleneck with higher end cards. You can always sell the 5750 later to help get a faster card.