I just have one concern my computer has a G-Force 3 video card from what i remember reading was that the lowest video card KR supported was a G-Force 3 Video card if i had anything less i do not think i could even play KR. my guess is SA may require more then a G-Force 3 video card to play but i do not know for sure does anyone know?
I checked the site for SA and I don't see anything on specs yet, but not trying to be a jerk and tell you to buy a new system but I have been going through the same situation myself not with a geforce 3 but on the same lines.
I had a geforce fx 5700 and wanted to up grade, that means its an AGP graphics card and well the problem is the price of a new AGP card is really high to what you can get. I got lucky and found one really cheap but its still a few years behind as for cards. Geforce 7600 gs so I should be good.
Now in my research on what to do I found that most motherboards have better on board graphics then what you are currently using, so it might be in your best interest to invest in a new tower, if you can. With that new tower you will also get the PCIe slot so you can get the new video cards which are cheaper then an AGP.
My suggestion is to find a good computer shop that builds them near you and get one built, stay away from the walmarts and best buy computers. If you choose to upgrade your current one your probably looking at on the lower scale of agp cards a geforce 6200 and then a new power supply. Not knowing where you live that could be a 100 bucks or more.
I did make the mistake and bought a new system last year but stuck with an agp card slot ones, it was one of the last motherboards that had them, I regret it now and should have just upgraded I would have saved alot of money in doing so.
Hope it helps, because its sounds like you looking to make a decision.