Windows 7 32 bit vista to 32 bit windows 7 memory problem

[BURNS81]

Hello. I just upgraded from vista 32 bit to Win 7 32 bit and i am noticing a problem with the memory management. I have 4 Gb in my system, but windows is only using 2GB. I understand that 32 bit systems do not use anything over 4 GB, but when i had vista it used 3.5 GB out of the 4. So why now have i lost 1.5 GB in usable memory when i upgraded to windows 7? Thank you for your help.