The time change should only apply for a second or two, then revert back. This happens with all installers of the BearShare 5.1 beta version because it was originally programmed to stop functioning by a certain date in 2005, but the one created by File_Girl generally causes the system less issues.

Was the archive called BSTESTINSTALLER 5.1.0.25c.rar or BSTESTINSTALLER 5.1.0b25? If not, you can get it here. Do a clean install.

If you are using Windows 7, you should right-click the installer and choose Run as Administrator. Perhaps if you do this, it will solve your problem.