I installed windows server 2008 on a new Hp proliant server.I just got to realise now that what I should have installed is windows 2003 server.I have tried formating the disk to no avail.Please,how do I uninstall windows server 2008 so that I can install that of 2003.

Why was formatting the disk unsuccessful? If you are trying to format the disk that Windows Server is installed on from within Windows Server, it won't let you do that. If this is the case, format or erase the disk using another utility outside of Windows such as DBAN on a self-booting floppy or CD. The existing disk partition can also be deleted, recreated, and formatted during Windows Server 2003 setup (which may be quicker and easier if using a RAID array).