Get yourself a copy of InformINIT, and either Symbionts or Conflict Catcher. The former is a searchable document describing every known extension, control panel and other System Folder add-on for System 7 and 8. The latter two are better extensions managers than Extensions Manager.

You might also want to check out System 7 Today, and/or their forum.

Step one of course: make a backup of your system folder in case you pooch it completely