This program might help (though if you take a RAM module out, it might have the amount and speed written on it):
That program will also be able to tell you the speed of the RAM modules running in your PC too, because you should get exactly the same speed of the stuff already in your PC, and if you can, Brand too (Getting a faster module than you have in there will just slow the newer one down to the speeds of the slower one (for example PC3200/DDR400))
Yeah, that card seems good by the way,
and if you have only 256mb, i would upgrade to 512mb. 1gb is also great, though most people probably wouldn't notice the difference unless they ran alot on there PC (I do notice a bit). One good way of checking would be to go to Control Alt, and Delete and checking how much RAM is being used up when your normal amount of programs are running. If you think it nears the borderline quite alot, upgrade, and with 256mb, you really should anyway.
I hope this helps