I was installing some small and short flouresent fixtures, and 7 of the 8 fixtures heated up just fine. But one tube kept blowing out as soon as i turned on the switch to energize the circuit. I went through three lamps like this. What would cause a tube to immediately blow when energized?

double check the wiring of the sockets from the Ballast or Ballasts. I have come across the odd flourescent fixture mis-wired from factory that could give you this problem.

I'd second that. I don't know about your fixtures, but some of our fluoros have the wiring from the end sockets brought back into the middle of the fitting, and it is possible for someone to have crossed the wires so that one filament of the tube is straight across the supply (via the ballast).

Otherwise, it could be something like a shorted ballast or starter.