The problem with phpBB (and the forum we use here at work that looks like it uses a similar schema) is that the tables are poorly designed. ESPECIALLY the user table. I just took a look at phpBB's user table and there is a TEXT datatype in that table (sig). blech. At least they took the text stuff out of their posts table. BUT the forums table has a text datatype in it.

BUT it is 3rd party software and you don't want to get into re-writing it unless you want to contribute to the software. What you need to do is get stuff happening in RAM.

By far the biggie settings for me have been:
table_cache, query_cache_size, query_cache_limit, thread_cache, key_buffer_size, with table_cache being the most dramatic change I made.

Did you get the mysqlreport perl script? I'm interested to hear what it's saying about your key buffer usage, your query buffer usage & your connections.

erin