(I agree with what Yippy said, first off)
I am relatively new to this, and the experts we got here might want to smack my on the backside of my head for this, but it worked for me, here I go anway...
I got the hose extenstion off a vacuum cleaner and attached the small brush tool to the hose, turned it on (duh) and removed dirt that way. sucked the filth off like a charm. Of course, this was not
my Powerbook, but it was a good friend's G3 desktop and assorted peripherals (keyboard was suprisingly dirty, ICK) I wouldn't do her wrong, not including myself, she is only the second Mac user I know in this city {{sigh}} we're a rare and intriguing breed it seems.
so long as the suction is not so powerful that it will dislodge small items, it should be fine. (e.g., shop-vac is a bit much I think) a simple vaccum extension seems fine, In my humble opinion.
A high pressure air hose (if you have access to one) should blow the rest away. be sure to cover things like the keyboard or what have you... don't want dust blowing back into there.
secondly, those Pledge "Grab It" dry cloths work really well for wiping dirt away. It alone can clean up a lot of crud. be sure not to get it caught on small items that will snag it, leaving a piece of cloth. that's no good. smooth surfaces are better here. they are not considered "lint free" but I think they're fine
within reason.
If you clean your TV and then hold the [clean] Grab It cloth against it (to statically charge it) it will get off the surface of anything...
DON'T do that on any inside parts of your computer though obviously. it just cleans your monitor, keyboard, tower (closed) and surrounding table top really well, without a lot of effort.
hope that helps. As always, use your common sense and caution.