Some info about the Radeon HD 2600 XT and PRO has been leaked. It appears that both cards use a 128-bit memory interface, just like the GeForce 8600 GTS and GT they are supposed to go after.
Another upcoming card from ATI is the RV610LE, this one will only have a 64-bit memory interface. This is a quite cheap card and it's very popular among OEMs.
ATI tried to keep this fact from the public eye for a while but what can you do if you want DirectX 10 below $70 with Shader model 4.0 and some cool video processing you will have to live with 64 bit memory. It saves AMD a few bucks per card as the Build of Material popularly known as BOM is smaller for the 64 bit memory card.