since Pathfinder is fully compatible with 3.5, if I wanted my Pathfinder wizard to become, say, a Master Specialist would he still gain all his arcane school abilities if he took the prestige class at 4th level or are they determined by class level rather than character level?
Alizor(Pathfinder Adventure Path Charter Subscriber; Roleplaying Game, GameMastery Maps Subscriber)
Unless it says character level the ability would be determined by class level. In the case you describe the specialist abilities would be determined only by wizard levels. However as 3.5 material, the Master Specialist would need to be converted. I can't remember off the top of my head, but it wouldn't be too difficult to convert the PrC to include a progression of the original Specialist abilities.
Just remember while converting that you do need to take balance of the classes into account. If the master specialist barely gives anything up to start the class, then the reward over straight wizard shouldn't be too large. You "shouldn't have your cake and eat it too" effectively.
Pathfinder is largely compatible with 3.5, but not all of 3.5 is compatible with Pathfinder. There are significant differences that need to be looked at for balance issues.