Creating a Ramdisk in Sys Memory under a Vista 32 OS

I have a computer that is running the MS Vista 32 bit OS. I have 6 gig of ram and can only access 3 in the os. Is there a way to load a sys ramdisk into memory prior to booting into the Vista operating enviroment? This way I can at least us the additional 3 gig of ram sitting and going to waste.