I'll tell you this, in my Vista 64-bit, it'll speed up the loading of programs, not necessarily speed up frame rates in FS.
Here's a step-by-step done by a dummy for other dummies with Vista.
As Moe says, Click Programs > Accessories > Run. But do noy type in Boot, rather type in msconfig.
When the MS System Configuration window opens, click the Boot tab.
When the Boot window opens, click Advanced Options.
When the Advanced Options window opens, check Number of processors and enter the number below as Moe say, 2 for dual, 4 for Quad. Next check the Maximum memory box, don't worry about a number, just check the box, a number will usually appear.
Caz