file already exists error (Registering DB)
You can find the temporary files in the directory specified by the TMP environment variable. If you go to the control panel, then System, then click the advanced tab and click on Environment variables, you'll see TMP under the user environment section.
There is an issue that's come up recently on systems that have Microsoft .net Framework 2.0 Beta installed where temporary files get allocated with the names of existing files. To temporarily fix the problem, you can run Windows Disk Cleanup and tell it to delete your temporary files. This is quite a bit easier than deleting them yourself because there are almost always files in use in that folder.