Does anyone here know how Fallout and Fallout 2 handled the gameplay? Like how it calculated successful uses of skills?
Did the fact that each skill was labeled as a percentage actually mean anything, considering they could all go well over 100%?

Yeah, the % where your chances of success. having over 100% means that you'll still get hit success rates even with lots of penelties.

IE your small guns skill is at 150% You using a pistol at long range *say penity of -20%* target is behind cover *-30%* it's night time -30%
So in this made up situation you'd still have 70% chance to succeed not the 20% change you'd have if you stopped at 100%. Everything has a difficulty penelty that effect you skill when you use it. After that it rolls a die and compares to see if you are successful.