Two months is way too soon to delete someone's name. Then people would be going, "oh no? has it been two months yet? oh no..." and they would post for no reason just to make sure the two months never comes from not posting...I would say clean out anybody over two months old without any posts, and everyone who hasn't logged on in the last year. Send them an email notification first, though...
Thats the same deal with hotmail. Hotmail deletes accounts after 30 days of no use. That is way too soon. The only reason I have that account is so I can play games at msn gaming zone because hotmail gives me a .NET passport, which is required for MSN gaming zone. But it also makes me frequently have to log into hotmail to make sure that they dont delete my name.
So two months is way too little of time. I would say at least 6 months.
The email notification is a good idea, however. That allows people notice just in case they have been incredibly busy for a period of time and not been able to get to the board.