According to the Strategy Guide, the top respawn limit for TIE Fighters in X-Wing is 156, so your memory was pretty close to correct.
As for the Hospital Frigate mission, It's Mission 4 of TOD I (I remember that Mission like it was yesterday) and it WAS A Bugger to pull off. It's compounded by the fact that the other three X-Wings in the mission are all part of their own flight - you can't order them to do anything or engage anyone.,
It's called either the Redemption Scenario, or the Requiem Scenario, and it's very very hard. So hard, in fact, that Rogue Squadron uses it as it's training mission in the Novel series.
There's actually a way to cheat at that mission, however. The Mission Completed Objectives only require the Corvette and shuttles to survive the mission...they do not have to dock with the Redemption. You can order the shuttles to go to hyperspace right at the beginning of the mission (make sure you only do it once) which only leaves the Korlov to dock with the Redemption.
Here's the way to tackle the mission though:
Step 1: Align yourself in formation with the corvette - it's the Fighter primary target. Wait for the Warspite (FYI: The Warspite is the name of the Nebulon B Frigate on this mission) to arrive. When the Warspite arrives head towards it IMMEDIATLY. It will jump out before you reach it. Put all energy from your ELS system into your Engines and accelrate at max throttle.
Step 2: Target a bomber. Any bomber. Doesn't matter which one. FLY PAST THEM. Turn around 180 degrees and slow to 1/3 thorttle. Lock onto each Bomber in turn at fire one JUST ONE torpedo at each bomber. Back to full throttle. Head for the Korlov. Ignore the TIE Fighters running around unless they are REALLY trying to kill you. Before you reach the Korlov, the Warspite will appear several kilometers beyond it. This time, it will stick around after dumping three more bombers and another pair of TIE Fighters into the mix.
Step 3: Head for the bombers. You have to take out at LEAST one on the head to head pass if you want to survive. Again, I recomend using torpedoes. You have six torpedoes on this mission and there are six bombers. Do the math. Corvettes can take up to five torpedo hits, anything over that will kill them. On the first pass each bomber will only launch 2 torpedoes, so if you take one out (or even force him to break off his attack) you will still be okay. At this point you should have two bombers left, headed for the Korlov, take them out. Then you can focus on the fighters....remember, at this point you're only goal is to stay alive long enough for the Korlov to go to hyperspace. It's already docked, and there are no more bombers on the mission, so you're pretty safe. If you REALLY can't bring yourself to destroy the bombers, bring them down to Hull Damage, and the hit them once or twice more with lasers, not quite enough to blow them up. This will send them back to their homeship to dock, and on this mission at least, they won't be replaced. This is not true so much on the later missions, but is a hard fact of the game: Ships with major hull damage will try to return to their mothership to dock.
Side Note: Attacking the Warspite triggers it to launch successive waves of four TIE Fighters (or maybe interceptors, I'm not sure) so be VERY careful about loose blaster fire near the Warspite. For future refrences sake, this is true on just about every mission with a capital ship on it. The game is scripted to have it launch new waves of fighters when you attack (not everytime, just the first time, but it replaces them everytime you blow it up.
EDIT: Also, in regards to Speardons post, there were no Missile Boats in X-Wing, unless you mean the Gunboat (which was always my favorite Imperial Ship), and the TIE Advances only really show up at the end of the game on the Death Star Missions.
Someone also mentioned firing while docked with a reload craft...I remember doing this too in TIE Fighter, but try it sometime in X-Wing Vs. TIE Fighter or X-Wing Alliance. The Reload craft explodes, and that can REALLY ruin your day.