The store that I am buying from doesn't stock the 256mb version, and I am not old enough to order online and my parents won't pay online either. If that was an option, I definately would though.
To quote my parents when I was younger:GET A DAMN JOB!!!!!!
The 7600GS should be good enough to last you 1 - 2 years depending on your expectations. AGP has been on life support for the longest time, but I would guess that by the time you want to upgrade to another video card you will have to upgrade your entire system.
Good luck and have fun.