Here is more details on the issues encountered when migrating from ColdFusion 8 to ColdFusion 9 on a Windows2003 VPS server:
"The 1st attempt the install failed completely at the end and broke both CF9 and CF8. I uninstalled CF9 and rebooted, CF8 was working again.

2nd attempt the install completed, but the settings migration failed. I had to follow this Adobe KB:
http://kb2.adobe.com/cps/527/cpsid_52797.html

After that, the migration completed fine."

My hosting company did a great job working out these issues.