Okay, all cards beyond the Radeon 9700 come in either 128MB or 256MB models.
BUT, all of the cards, I repeat, ALL OF THE CARDS beyond the 9700 (except SE versions, I think) are 256 Bit. I'm not quite sure what the 256 Bit means, but hell, I know it gives you better graphics.
The Nintendo 64 was 64 bit, the Xbox, PS2, and Gamecube are 128 bit. Look at the graphics on some Xbox games. Now, imagine what your 9700 Pro, 9800 Pro, and 9800 XT can do when developers unlock their full potential. Which we may never see if the card manufacturers release new cards before these get their chance to shine.