Sounds like they might be the same variation on two essentially similar knots. (A bowline is simply a sheet bend that's tied in a different fashion and for a different purpose - instead of tying two pieces of rope together, it ties one piece of rope to itself.)

To tie a "non-inverting bowline" (this is the terminology that Mors Kochanski uses), tie a regular bowline but the 'rabbit' goes around the 'tree' twice before going back down the 'hole'. Apparently, under certain conditions, a bowline can "invert" and turn into a slip knot; by taking a second turn around the standing end, this is prevented. If you can figure out how to do that, then you should be able to tie a sheet bend the same way.

But I don't believe these are the knots you're talking about; I suspect you're talking about the double bowline:

http://www.chockstone.org/TechTips/Bowline.htm

and the double sheet bend:

http://www.troop7.org/Knots/SheetDouble.html