Virtual CloneDrive works well. www.elby.ch
Not only is it also free but it is easier to use than the Microsoft one.
Also useful for writing/creating CDs to/from ISOs is the ISO Recorder Power Toy (for WinXP). For free as well! http://isorecorder.alexfeinman.com/isorecorder.htm
It extends the Windows CD Recording Wizard to allow you to right click an ISO to write it to CD, and vice versa.
Awesome! Thanks, Andy!
Both of these are great products. Personally, I use VaporCD (http://vaporcd.sourceforge.net) which is free. It allows me to create ISOs from CDs as well as mounting ISOs. And it's free.
Of course, YMMV.
Alcohol 120% and 52% are worth looking at.http://shop.alcohol-soft.com/en/alcohol_info.php
I'm glad someone else out there uses the awesome power of WinRar for iso's too - it browses em like big zip files! excellent!