Hi newcomer and welcome to the Tom's hardware forum.
For me, ur question isn't clear.
If u have Vista 32 bits, ur usable RAM will be 3.25GB, independent of the RAM that support the mobo.
When u install the x64 bit OS (Win 7 x64 in ur case), the amount of that usable change to the amount of RAM supported by the mobo. In that case, the x64 bit OS don't have a limit of 4GB of RAM.