Not sure if it'll help or not, but try upgrading your b2evolution to 1.9.3 or maybe 1.10 if you're into being an "early adopter".

Unfortunately no can do - there are too many templates that would need to be updated.

I found a partial answer - the new php install had memory limits set too low. I can now see the list of installed plugins. However clicking on any of them gets:

"An unexpected error has occured!

If this error persits, please report it to the administrator.

Go back to home page
Additional information about this error:
We need the PHP Tokenizer functions to get the list of Plugin events (Enabled by default since PHP 4.3.0 and available since PHP 4.2.0)."

I am running PHP5 with everything default (except for the memory limits I just increased).

I have resolved this issue. For anyone else who deals with this type of upgrade, the solution was:

Increase php memory limit (default is 8, I went to 20).
Having the "php5" package installed is not enough, you also need "php5-devel". I also installed "php5-tokenizer" at the same time as devel but I doubt that was what fixed it.

So ultimately, it had nothing to do with mysql!

Cheers