I want to create a popup survey on a vbulletin forum I own, just like you get sometimes when you go to Microsoft and they ask for feedback.

It would:

1. Popup a small window to say 20% of the visitors, using a dhtml window or similar.

2. It would ask if they wanted to help with our survey, with a Yes or No.

3. If they clicked yes, they get taken to a standard webpage with my survey on it.

I know there are subscription services like SurveyMonkey but I am using LimeSurvey since it is free and I have it installed. Its just the popup thing I would like to get done, without needing an expensive popup product if possible!