note: This advice applies to Acrobat v7.0.
You will need the full version of Acrobat to do it, for starters, which allows you to save and edit documents. You open the first page PDF, then drag and drop the rest of the individual pages into the page thumbnails area. Then do a Save As from there and apply the desired amount of file size reduction using "File: Reduce File Size" or "Tools: Print Production: PDF Optimizer?". The pages must be in PDF format, not TIF. You can open TIFFs in Acrobat, but you can't drag new TIFFs in to make a multi-page document. Annoying, but that's the way it seems to work.
A hint for getting the pages in order: Make sure they are named in sequence, 01, 02, 03 etc. and sort the Finder window in reverse order from last page to first. Then drag them into Acrobat. For whatever reason this causes them to be inserted in the correct order. It might also be affected by Date Modified, I am not sure. I use PathFinder and always Touch the date for the whole list of pages and reverse name sort before dragging them in.
Kinkos or similar may have copiers that can generate multi-page PDFs. I don't have much experience doing that, but I do know one of the copiers here has such a function.