Before anything else, understand that, while it may have long ago, changing the dedication in BIOS doesn't accomplish anything (anymore). The dedication in the BIOS only applies while the BIOS is running; it doesn't pass this information to the Windows-based driver.
If you look back through old conversations (sorry, I didn't keep track of where, so you'll have to search), there were instructions for making changes, via the registry, in the amount of RAM dedicated at driver initialization time. As Al said, this will happen at runtime automatically, so this isn't usually necessary - and can adversely affect the overall performance of Windows. The main reason we hear about for wanting to make such a change is if a legacy game will refuse to run because it sees the dedication as being too small. This is a bug in these games and should be addressed by the game designers, not by making a change like this, but the game designers often refuse to revisit legacy games, unfortunately (I say they should be shamed mercilessly for making such a stupid mistake and not being willing to fix it).
...S
