[_ck_]

Running bbPress on a server with 128mb of ram would be very difficult unless it’s a very light setup with low use.

256mb should be doable if that is real, permanent memory and not burst memory. It’s also important if you don’t have alot of overhead like cpanel running.

#1 problem on most small VPS is you either don’t have the mysql cache turned on or it’s too small of a cache

#2 problem is you almost certainly don’t have a PHP opcode cache like eAccelerator installed

#3 problem on almost all VPS is bad neighbors.

On a shared host, you can easily tell when you have bad neighbors who are overloading the server (node). On a VPS they are hidden. If you have an inexperienced host, they may have a hard time tracking down the offender, or may not even care. If they tell you that your neighbors can’t affect you, that’s an outright lie or plain ignorance.

If you are running bbPress 1.0 alpha it has several problems generating far too many mysql queries and that could be causing you some headaches. If you are using bbPress 0.9, definitely stick with that, but you need to fine tune your settings.

WordPress has some nice caching plugins like wp-super-cache. No such creature exists yet for bbPress, so all pages must be rendered each time by the engine, making it use more overhead than WordPress.