How to mount a CD or DVD image file as a virtual drive
Free tools to mount an ISO image on XP or Vista
MagicISO is great and it's freeware. It has a 32 bit and a 64 bit version and it also runs on Vista x64 :).
Free but doesn't work on 64bit Vista.
Fantom DVD Virtual C/DVD-ROM
Tools to mount an ISO image that contains spy/adware if you don't pay for it
Warning: Not free anymore now you are forced to have spy/adware
Warning: Not free you are forced to have spy/adware