I'm working on a survey now that asks people to compare two places. I have over 2,000 different pairs, so I'd like to divide this up into many different versions of the survey, so that each person will only answer about 120 different questions.

My question is how do I make it so each user gets a different version when they access the same site?

I want to control for which pairs each subject sees-- that is, drawing up 120 random pairs from a list won't do. I will use excel or some perl script to come up with the quasi-random, counterbalanced, list of pairs for each person, and I'd like to be able to input this information into the site.

Any suggestions?