Hi Lorraine,
a happy new year to you.
Start off by searching around for good theme sites like
Vista Themes - Free Windows Vista Themes
Download them to say the My documents folder.
Go to the Control Panel from the Start menu.
Select "Appearance and Personalization," then go to "Personalization."
Select "Theme."
On the dropdown select browse and browse to the folder where you saved the theme.
click "OK."
Hope this helps,
regards
Steve