Personally either program will do the trick for you. I think photoshop cs3 throws out better results but it really comes back to what you input. If you throw a single JPEG into photomatix and have it "fake" HDR it will look better then in PSCS3. However if you lock off your shot, correctly do the RAW series of three, and correctly over/under/correctly expose it you will get better results out of CS3.
Either way HDR is a little bit of a fad I personally think, its pretty cool what you can do with landscapes but really I dont know if its worth buying a program just to do it. Listen to the guys above and grab a demo version somewhere and test it out first.