[orban]

You can use a load balancer for example.

I don't quite understand why you come here and ask for help but refuse to actually explain what your problem is.

You ask "i want to move onto 2 servers, will this help with the database crashing due to overload?" but don't explain WHAT actually the bottleneck is. You say you run vBulletin then you tell me you run Icecast with vB as an authentication service. How is this bridged? Maybe your implementation is the bottle neck, an easy edit of the script can fix that. Maybe your apache/php/mysql config files are the bottle neck, again an easy edit can fix it.

Adding more memory certainly will NOT help the issue because your database size isn't even 2gb. Are you swapping during those peeks?

Checking if a given user/pw combination is correct and if a user is in a given usergroup is ONE (1) SELECT query on the user table, you can probably run 500/second of those on your server (if that's the only thing it does).