Where do i get an HTC-Hero ROM
It's probably rooted.  If not, then it was in order to install 2.3, and it can be rooted again.  If you have the SuperUser app, that should be a clear indication that it's rooted.

You should definitely be able to downgrade.

The best source for ROMs is generally the Android Development subforum for a particular device on XDA.  In this case, this subforum.