I am in the process of planning a real estate website and we've come up against a bit of an unknown regarding giving search results to a user:

Say the visitor has performed the search and now has a page of results in front of them. When they click on the link to the property is it better to have (a) a javascript window pop-up with the details, leaving the query results still in the parent page, or (b) is it better load that particular property's details over the top of the query results?

I ask this from the point of view of
1. would the user get confused that there are now two pages in front of them (though I think people are getting used to more than one window now?) and;

2. from a design point of view: If the details are loaded over the top of the results can just hitting the back button or clicking a javascript history.back() link bring them back to were they were wiothout having to run the query again? ... on all browsers/platforms?

I also guess that this method is neater then a pop up but I am not sure is best mainly from a PHP query point of view.

Any help, comment, or better ways of doing it appreciated.