I once faced a similar issue and actually ended up running another installation on a separate server and monitoring the changes made by the install using regmon and filemon. Using the reports I then cleaned up the original server by removing the remaining files/folders and registry keys. Mind you, it's probably not an optimal solution - it was a mammoth task as it took me most of the day to trawl through the regmon/filemon logs and remove any left-over files/regkeys. I didn't have a choice though and in the end it did do the trick :)
If your installation goes through but you get the configuration database error you might want to scan your registry for the name of the database and remove all the references (e.g. on my server it's HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Shared Tools\Web Server Extensions\12.0\Secure\ConfigDB\ ). Hopefully this should prompt the wizard to create a new database.
Good luck
Regards,
Greg Osimowicz