by default it will share 64 mb from ram ....
to change it .. u have to go to bios setup and change it from there.
start the pc ...
press "del" when bootscreen comes up to go to setup ..
Goto the second menu option on top (Advanced)
then the from option (Chipset)
then change the second option (Frame buffer size ) to the required value (16 MB, 32 MB, 64 MB,
128 MB, 256 MB) .. according to ur requirement .....
hope it helps ...