Without delving into the Linux/Windows Apache/IIS debate, Moodle will run on all of them. Sounds like you don't have a choice, perhaps.
To move your site:
1. Install IIS, MySQL, PHP on Win Server 2008. Phpmyadmin is also useful if you don't know the MySQL command line.
2. Backup existing moodle root directory (/moodle by default).
3. Backup existing moodle data directory (/moodledata by default).
4. Dump existing MySQL database to .sql file.
5. Restore moodle root directory on Win2008 IIS server.
6. Restore moodle data directory on Win2008 (outside of moodle root for security)
7. Import .sql file in new MySQL instance.
Linux/Apache really is a better platform (I've had great luck with both Debian and Ubuntu), but sometimes you're not allowed to do that. I've run Moodle quite successfully on Win2008/IIS.
Be glad to answer questions as you do your migration.
moodlewright
