It seems to be pretty common for people to get stumped in trying to remove their SharePoint Server 2007 installation.
This is in no small part due to the fact that the uninstaller simply quits without any message unless you ensure a few things ahead of time.
1. Remove Server From Farm
In Central Admin, Operations tab, Server in farm — Remove server. You’ll probably get an error message after you click remove, since the server isn’t able to render the page anymore.
2. Remove Databases
Content DB, Config, Search, SSP, Etc.
3. Remove Web Applications
Use the IIS Management Console, remove all web applications related to the MOSS site.
Now you can remove MOSS via add/remove programs.