Halo Ops is once again trotting out the old "Halo 1.5 with XBL support" rumor, as late as the end of last month. This time not only does it have the mandatory "a Microsoft rep confirmed" bit in it, but the poster, Tycho, claims to have discussed it with Randy Pitchford, who says Gearbox wasn't involved.
That makes complete sense, of course, when you realize that Xbox Live is, of course, for the Xbox, not for the PC, and Gearbox was only involved in making the PC port of Halo. Also, it's hard to be involved in something that Bungie has said over and over again doesn't exist. Who knows, maybe they've changed their minds, but the logic used when they denied it earlier still holds-- it would just slow them down from finishing Halo 2, and as a result doesn't make much sense. You can, of course, as always consult the Bungie Rumor Control Database to refresh your memory.