You could build a page large enough to hold both sides in one file. For instance, one sided file = 8.75" x 11.25" ( includes bleed ) or whatever size you're working with. Your file would be 17.5" x 11.25" with both pages "butting" eachother. You should get more specifics ( such as "work and turn" ) from the print vendor, perhaps they could supply you with a template. You could do the file in any page layout program, including Illustrator. But, the vendor should be specific in what exactly they are expecting ( i.e., bleeds, folds, scores, trim amrks, etc. ).
The printer probably has AI CS 4 and there this would be no problem just two artboards in stead of a tiled file which would difficult if it ha bleeds.
Where as in CS 4 which is made for this type of situation.
So if the printer is asking for this then they have CS and that is your answer.
I know you are asking about CS 3 but sometimes an upgrade is unavoidable and if you are going to get this request more often then why not?