MagicISO Virtual CD/DVD(MagicDisk) is a FREE utility that loads a TSR and lets you mount an ISO file as a Virtual Disk. So if you for example have the Windows XP SP3 OS ISO you can mount it virtually and then install it easily into a VM without having to burn a disc! Truly Magic!
There is also an ISO extractor that lets you extract the ISO to your hard disk.
The company also makes a very neat for pay program called MagicISO Maker which allows you to create ISO files and also convert them. The combination of these two programs has almost eliminated my need to create CD/DVD's of my ISO files! No More Discs laying around! How green can you get?