I just found this info within Reef Central's archives:
250w example:
Probe start: ANSI: M58, core, capacitor
Pulse start: ANSI: M138, core, capacitor, ignitor
HQI: ANSI: M80, core, capacitor, ignitor
EYE: ANSI: H37, core, capacitor, actually a mercury vapor ballast
Electronic: ANSI: none, metal box with wires
probe start will run american bulbs with ignitors built into the bulbs like coralife and venture bulbs. some german and euro bulbs will run fine on these, but without an ignitor, the bulb struggles to light and bulb life may be decreased. also reliabilty goes down.
pulse start will run the german/euro bulbs (ushio, AB, radium, etc.) these bulbs don't have built in ignitors, so the ballast has the ignitor wired into the circuit. the ignitor provides the high voltages needed to fire the bulb. you can run probe start bulbs on these ballasts, but the two ignitors may try to fight each other and possibly cause a fire.
HQI ballasts are similar to pulse starts in their wiring and ability to run bulbs. the output is a little higher which is meant to run the double-ended bulbs (commonly called HQI bulbs). people run mogul bulbs on these and they run a little hotter and brighter because they are being overdriven. this in turn shortens the life of the bulbs.
So based on the above info, would it be a safe assumption that an M138 could take the place of the M80 ballast? I think that I read somewhere on Reef2Reef that it could but may underdrive the bulb.
