Use either the 1.20RC from LL, or the Coolview built by Henri Beauchamp. The links to the coolview patches are along the left hand side of the blog.
Before installing this version, clear your cache, that is in edit->preferences->network.
After installing, and when first running the new client, at the start up screen, before logging in, go to edit -> preferences -> graphics. Click "custom" and then set everything to minimum and turn imposters off. When you run the new client, gradually add features until your hardware is happy with what you are doing.
This will allow building up to 768M directly.