I'm surprised with the replies I'm getting here. Thanks guys!
My current config is - 1.8 Ghz intel Dual core, 2GB DDR2, 80GB HDD and of course the 8600GT.
The system is already maxed out. It doesn't support more than 2GB RAM and both the PCI slots are full with a firewire extension and another Ethernet port.
I considered upgrading, but there's nothing left, really. At the moment, I'm either going to get a new desktop or a laptop. I'm debating on how to go about it. (I seem to move around often, these days)
-chronodekar
The CPU you have sounds fine, especially if you get a motherboard that will let you overclock it some.
Personally if I was in your position this is what I would do.
Go to the For/Sale trade forum here or another site or use ebay. Get rid of your current motherboard, heatsink, and video card. Dump all 3 pieces. You might get about $10 each and that would be fine. Might get $20 for the motherboard.
After that, take that $30 or so you made selling those parts. Find a decent, but cheap, motherboard for your current CPU for sale used. Look around. I'm not sure what dual core intel processor you are using but it should still be good enough for even modern games. Hell, I still have put together some Opteron 165 systems that I OC and run modern games just fine.
Anyhow, upgrade the motherboard, and heatsink as cheap as possible so you can overclock. Learn the limits of that CPU and give it a little juice. Whatever you are using, I'm betting you could at least hit 3 Ghz easy enough. Also make sure the motherboard has a PCIe slot. Lastly make sure the motherboard you upgrade to supports your current memory, assuming it is at least DDR1. If your current memory is DD2 that is better as it is cheaper to find more DDR2 than DDR1 right now.
Next look for a good video card upgrade. With the right deals on new or a used purchase you can get a 4650, 4670, or even a 4850 pretty damn cheap.
Done right, you could probably upgrade your entire system for about $50 to $75 and be able to play any PC game on the market. Some settings you might need to turn down, but all games would be playable and still look decent.
If you could provide more detail about what you current have I could even give you a specific list of what you need to do and how much it will end up costing to do it.