I'm on Win 7 64bit and I only have 4GB of Ram. In CS5 it indicates that 2.5 will be dedicated to Premiere and 1.5 will be dedicated to other programs. When I try to change the amount of Ram (increasing the amount to Premiere/lower the amount for other programs) it does nothing.
Is It possible to access more than 2.5 GB of ram for Premiere with my current setup?
Taking memory away from other software means taking away memory from such things as the operating system. You really, really don't want to go too low with that. It would also cause your applications to fight over RAM, causing RAM contents to be swapped to the hard disk, which is one of the worst possible things to do to your performance.
If you want more RAM available to Premiere Pro, then install more RAM.