My guess is, you install Conky, which makes it possible to run top command, and then you open X-Terminal, and just type "top" and hit enter.

-Edit-

Though I'm not sure how productive that would by while your N900 is slow enough to take minutes to respond to clicks. *shrug* If you're up for it, that may help shed some light on this, but it may just end up wasting your time. Up to you, basically, but may be helpful.