Thanks for the pointers. Posting to multiple forums definately sounds like a good idea. I suppose I could just post to a number of forums but if you would like to suggest some specific forums, I would be happy to consider them. If you know something about the user demographics of these forums, even better.
As for relevant computer usage habits, things like avg. hours spent on the computer a day might well be of interest. Familiarity with multiple OS's. Things like that.
Oh and indeed, thanks for the interest for participation but a) the study will not be running just yet and b) since I've already been discussing the study here (even if very vaguely) I may start from other forums when I really start looking for the participants. If I'm having trouble finding any, I might still come back here, too