Hre are the specifications:
Dell Precision 670
2x 2.8 Dual Core Xeons (4 cores total)
4GB ECC Ram (16GB max)
150GB 15k Raptor system drive
500GB Swap/storage drive
160GB hardware raid. 2x 160gb Raid 1
PNY 9800 GTX+ 512MB DDR3
Dual layer DVD burner
600 W power supply
I think this particular model supports two graphics cards but not SLI. I only have one card, currently. Any thoughts?
That is a fine system for mining, with possibly the power supply being an issue if you want to run 2 cards. You need around 25 amps on the 12v rail per card. So 50 amps total if you want to run 2 cards. Most older power supplies have a lot of their amperage on the 3.3v and 5v lines but not on the 12v lines. Yours may or may not be like this.
Also, you need to find out what version the PCI-E slots are. A lot of motherboards with v1.0/1.1 slots will not recognize the ATI 5000/6000 series cards. Some do, some don't. You might have to chance it if you have v1.0/1.1 PCI-E slots.
Mining is all about using ATI video cards. The rest of the system does not matter. As long as the motherboard has PCI-E v2.0 slots then you are good. Crossfire/SLI is not needed in mining. Potential cards are 5770, 5830 or above, 6850 or above, 6950 or above. The sweet spot right now with available cards through places like newegg is probably 6870's or perhaps 5770's, depending on how much you want to spend. If you can find 5830's for a reasonable price they are the bomb. Sold out most places though.
BTW, if you haven't guessed, your NVidia card is pretty useless for mining.