02/04/10: Just about every browser I can think of has tabs - and there is a good reason for that (I often have more then 70 tabs open at one time). So, why can't a Finder (Mac's file browser) have tabs? ...well, now it can.
Try TotalFinder - it's free and easy to install and use.
Mac users have been asking for tabs in Finder for a very long time, but for whatever reason, Apple doesn't find that feature important. That, and the way it handles window resizing/moving.