Ok, sounds like you made some attempts to install the SMP client before you installed the graphical client. Perhaps there's some fah process(es) from the SMP install that's interfering with your graphical client.
1) Go to control panel and under the programs icon you will see "uninstall a program". Tell us what you see there. If you see "Folding@Home Windows SMP client", you need to uninstall that program.
2) You could also start the Windows Task Manager (Ctrl-Alt-Del then choose start task manager) and then click on the processes tab. Click on the show processes from all users box at the bottom left and then click on the "image name" heading to sort them in alphabetical order. Check out the fahcore_XX.exe running (high cpu use) and other fah processes running and get back to us
I'm just trying to find out if you are running a "clean install" of the graphical client.
If it is a clean install then there's another possiblity to consider.
1) When you installed the XP graphical client, you chose "small WU; less than 5 Mb". These WU's step faster but you get less points.
2) When you installed the VISTA graphical client, you chose "large WU". These can take much longer to process (longer step times) but you will receive more points per WU (up to 500 points).
Let us know what you see🙂