OK, how doe I remove/install one of these things?  Is it necessary to remove the gas tube?  TIA

Typically the tube is seperate from the barrel nut. So you just unscrew it from that. Assuming you do not have a front sight assembly, but a flat top AR using a scope, after unscrewing the tube just slide it off the end of the barrel. Sometimes you can get a good enough grip to unscrew bare handed. If it's too tight use a strap wrench.

First, are you removing or installing. Second, there are 1, 2, and 3 peice free float tubes, which one do you have or want.  Third, yes the gas tube has to come off along with the the front site if you are going to remove the free float tube from the barrel.  Last you can not have a break or anything on the end of the muzzle that will prevent you from removing the front site/gas block.

Actually, I'll be removing and then installing.  I have a Bushmaster V Match with the factory aluminum free floated handguard, and I want to replace it with the Hogue free floated aluminum handguard.  It looks like the Bushy is a one piece, and I believe the Hogue is a two piece unit.  The V Match has the milled front sight/gas block assembly, so I don't have to worrry about getting over the front sight.