To uninstall IIS on Vista:
Start -> Run -> appwiz.cpl -> Turn windows features on or off -> Internet Information Services (uncheck and click ok)
On Server 2008:
Start -> Run -> appwiz.cpl -> Turn windows features on or off -> Server Manager -> Roles -> Web Server (IIS) -> Right click and select 'Remove Role Services'
Regards to PHP, just delete your PHP folder and the php.ini file if it is in a different folder.
Thanks,
Mukhtar Desai
IIS Performance Team