Most BIOS support the specification of some amount of dedicated memory for graphics buffers. I can't answer whether your's does as you haven't identified your board manufacturer. Now, that said, this is actually not necessary -- and it is very important to understand that dedicating additional memory will NOT improve graphics performance. The graphics drivers will manage this automatically, and use up to 50% of available memory, based upon needs of software being run.
Note: If you have software that is refusing to run because there is not enough dedicated video memory, then this software has a bug in it. Contact its developers to get a fix.
Hope this helps,
...S
