the extra 256 memory will be useless, at least nowadays, maibe in the future it will become handy, cause no game uses as much as 256mb of video memory....
The 256MB DDR might be a little much but can't hurt. Never know what future games may bring. Perhaps DOOM III will take alot of video memory. This card has a 325MHz core(same as the Ti 4600 I believe) and is DirectX 9.0 ready. Looks good for the price IMHO.
256 memory will come in handy with games such as Doom3 and HL2. But its not worth it with that card. For that money you can pick up a radeon 9700 that is many times better.