Well, I've had my other bulb plugged in for over an hour. So far no flickering. I'll leave it in for a couple of days just to be sure, but so far it looks like the bulb is the problem. The bulb I put in for this test is my old Aqua Connect 14K, which seams to still be in fairly good shape. There isn't even burn marks or however you describe the usual discoloration on the inside bulb thing, or whatever you call it.
So I might just keep it in there. I left a message with XM regarding warranty on the bulb, so we'll see what they have to say. J&L, where I bought it, wouldn't even talk to me about it.
If this bulb starts to flicker, and it is my ballast, I might just switch over to a T5 fixture for the same price as a new ballast. But thats another post all together.