I usually advertise studies here:
http://cbdr.cmu.edu/experiments/index.asp
Or on cmu.misc.market and cmu.misc.market.experiments on the CMU bulletin boards.
The experiments website has directions on how to get access at:
http://cbdr.cmu.edu/r_scheduling.html
If you want to put up a survey and not an experiment, what we usually do is just create a single slot, say at 3:35am a week from now, and make 300 openings at that time -- and then in the sidebar I put the URL and tell them not to sign up but to just go to the URL to fill out the survey. Then I check occasionally and if anyone's signed up I cancel them and tell them to fill out the survey instead.