First off, have a look at this page, which is a little blog post on performance tuning Windows 7 for virtualization. Seems like it might be helpful.
Second, the only Microsoft-supported way to do what you want is via a user profile customization, process documented in a Microsoft KB here.
Third, as suggested by @Zordache , setting registry keys is a function that's natively handled by GPPs (Group Policy Preferences), which is probably a better approach to this than GPOs.
Finally, if you insist on doing so via a GPO, your best option is probably going to be to use a logon or startup script that sets the registry keys in question. For the most part, they're the same as the key values in XP, but you should be able to do your own Googling to get precise key values for the precise options you want to set.
I suppose that in case the link goes dead, I'll post the registry keys and values for the majority of the settings below. Grabbed from the third link there.
;0 = Let Windows choose what’s best for my computer
;1 = Adjust for best appearance
;2 = Adjust for best performance
;3 = Custom
;Use visual styles on windows and buttons (0=off 1=on)
;Use common tasks in folders (0=off 1=on)
;Show translucent selection rectangle (0=off 1=on)
;Use drop shadows for icon labels on the desktop (0=off 1=on)
;Use a background image for each folder type (0=off 1=on)
;Slide taskbar buttons (0=off 1=on)
;Animate windows when minimizing and maximizing (0=off 1=on)
;Show window contents while dragging (0=off 1=on)
;Smooth edges of screen fonts (0=off 2=on)
;Smooth scroll list boxes
;Slide open combo boxes
;Fade or slide menus into view
;Show shadows under mouse pointer
;Fade or slide tooltips into view
;Fade out menu items after clicking
;Show shadows under menus
;(All off = 90,12,01,80 All on = 9e,3e,05,80)
“UserPreferencesMask” Is tricky because it’s a combination of all the settings, depending on what you pick, you will create a different hex.