are there any utilites that can convert a zip file to an iso file.

Are you saying that you have an ISO file that has been zipped?

You can use any unzipper to unzip it. XP will do that. Right click & choose Extract to:

There is also this freeware that I use:

http://www.ultimatezip.com/index.htm

If you want to subsequently burn the ISO to disk you can use this freeware:

http://isorecorder.alexfeinman.com/isorecorder.htm