There were Mac versions, however I believe they were designed with System in mind, rather than Mac OSX. As such, assuming you can find a legitimate copy (its long out of print in the Mac format) of the game you may have trouble getting it to work even with Rosetta.
So you're left with getting the PC version to work. Fallout 1 was originally built for both Direct X (Windows) and DOS, you may be able to get the DOS version to work under Dosbox, but I've not heard of it being done and the graphics are slightly worse than the windows version. You'll need to find a CD version to ensure this is going to work. Fallout 2 was only built for Direct X, so this option isnt going to get fallout 2 to work.
The simplest option, and the one I have to recommend the highest is to bootcamp and install windows and then simply buy from gog.com or Steam. If you've got a Macbook Pro, it will even run new Vegas well (I'm using the high settings). This has the disadvantage of having to buy a windows license. Of course this leaves out old Powerbook users.
If this isnt to your fancy, or you're running a low powered macbook, you may want to try CrossOver Games. They've given Fallout 1 and 2 a Gold Medal for compatibility (expect to install and run with only minor bugs) Tactics and Fallout 3 get silver (Usable, but buggy) and new vegas gets bronze (Installs, runs, and accomplishes part of its intention) However even with their gold ranking they still appear to be officially unsupported. As with all emulated environments you're starting to make things a little more complicated than they should be, so you're going to lose performance, and you are going to have to pay for it. If you're running an old Powerbook, you need not apply.