Is Leopard running on your iMac now? What edition of Vista is installed in
the Windows partition?
Bootcamp 2.0 that comes with Leopard does NOT create a cd with drivers for
Windows. The Leopard dvd itself contains the drivers for XP and Vista x86
and the drivers are installed by simply inserting the Leopard dvd while
Windows is running. If your son installed the 64bit version of Vista,
however, I can see your problem. The Windows drivers on the Leopard dvd are
only for the 32bit version of XP and Vista.
You can delete the Vista installation and reclaim the partition used for it
by simply running the Boot Camp assistant (in OS/X) and selecting "remove
Windows" (or similar wording).