The tab display properties is the 4th one from left. There will be the ' "windows and buttons" menu in it where you can select Windows Classic or Windows XP-style.
Select Windows XP-style.
If you can't find the Windows XP-style in there -- only the windows classic, tell me afterwards.
Also check next:
Go to start > run and type: services.msc
Search in that list for themes and check if it's running. If not, click start the service.