Providing the resultsets are in a similar format this shouldn't be a problem at all...
Best way IMO is to use XML as your structure for holding your search results then you can use XSL to format the return. Actually if you did it this way it wouldn't matter if the results sets had different columns and the like returned...
Simply put,.....
You have a page that gets the search criteria (say search.asp) and passes it to searchresults.asp.
Search results determines what search criteria has been selected/used, performs the search using that criteria and then formats the results using the appropiate XSL.
Does this help at all? Perhaps if you can give more info on the problems you are having I can help more.