Are you using 32 bit or 64?
If 32, then you can never get access to all 4GB of ram -- and even then, you have to enable the 3GB switch.
http://www.vistaheads.com/forums/mic...tch-vista.html
Switch to 64 bit OS, if you haven't already. Its the best move you can make. Trust me, once I did it, I knew I could never go back. I have 12GB of ram on my main computer, and sometimes thats not even enough.