To install on a Vista machine, you must be using either the administrator account or an account with admin privileges enabled.
Scroll down to 'Other Topics' here for a bit more info:
http://thesims2.ea.com/help/detail.php?help_id=281Also, as it is a duo core machine, take a look here about the possibility of altering the affinity settings in case you have other problems:
http://modthesims2.com/wiki.php?title=Game_Help:Dual_Core_IssuesAlso, you didn't mention what graphics card/chipset is installed on the machine. It may not be readily capable of handling the game (or may not be readily capable of handling more than the basic game). Even so, installing any newer or updated drivers for you machine's graphics card is is Good Thing.