Indeed, I am very serious about mining, and am looking at ATI cards that can produce 24x the mhash performance of my card!  According to the hardware comparision link that was posted - AMD/Radeon 5970 can produce roughly 700mhash/s!  I may purchase 2, however I think I will have trouble with my current motherboard [M4N98TD EVO has nforce n980 chipset].  I may get an equivielnt with crossfire chipset!

I still have windows 3.1 on small dedicated HDD, never use it though unless i need a good laugh.