Did the machine come with Vista or is it one you upgraded from Windows XP? If the latter then does it meet the hardware requirements for Windows Vista?
A good indicator of the performance you can expect is to look at "Control Panel\Performance Information and Tools". Have a look to see if one of the subscores is very low.
If you think the machine should be up to the job then there may be some software applications installed that are slowing the machine down. To check this out, bring up "System Information" (msinfo32.exe) and look at 'Startup Programs'. You can run this from the start menu (accessories, system tools, system information).