Hi,
Don't know if you're still trying to get it to work; activity on this module seems quite stale.
In any case, I recently discovered that the latest version of Apache-GDGraph available gave me problems with mod_perl under Apache2. My solution was to port the APIs used to a local version that used the Apache2 mod_perl APIs instead of Apache1's. I would be willing to consider making my new version available if there is sufficient interest.
I'm not sure if that helps you or not. If you're still having the problem and care to post the specific errors you're getting (from your apache error log), as well as the versions of Apache and mod_perl that you're using, I might be able to offer further help.
Best regards,
ptd