Yeah, I put the tire half on, then the tube. You can lay the wheel flat and gravity will help the tube parts you've pushed in, stay in.

EDIT: yeah, this was also posted before me -- but it bears repeating and repeating and repeating

Once you put the 2nd bead on, go all around that bead, pulling the tread to the other side so you can see in, and be sure you see nothing but rim tape beneath the bead. If you see any tube at all, you're headed for a pop. Make sure to jam the valve stem back into the tire so that the rubber gusset on it is above the beads. If it gets trapped between the rim and bead, you'll get a flat there too.

I'm talking about steps 7 & 10 here:
http://www.hostelshoppe.com/tech_tire_installation.php