Command to reset the sharepoint databases, if u r reinstalling Sharepoint

Click Start, click Run, type cmd in the Open box, and then click OK.
At the command line, change to the following directory:
\Program Files\Common Files\Microsoft Shared\web server extensions\12\BIN
At the command prompt, type the following command to create a new configuration database:
psconfig -cmd configdb -create -server ServerName -database ConfigDBName -user Domain\User -password Password
Rerun the SharePoint Products and Technologies Wizard.


http://support.microsoft.com/kb/927156