Bret:
DME is Dry Malt Extract
LME is Liquit Malt Extract
These are the sugars we use to brew. Either is fine for brewing extract.
Ryan:
If you used dry yeast and made a yeast slurry (dont worry if you didnt), you should get fermentation starting within 24 hours.
If you used liquid yeast and didnt make a starter, it could take up to 3 days for fermentation to begin.
Also, did you boil all of the water or did you do a partial boil? Most beginners will boil 2.5-3 gallons of water/extract and then top off their fermenter with the additional 2.5-3 gallons of cold water. This serves 2 purposes, 1, it lowers your wort temperature quickly by the addition of cold water. 2, it ensure's you get that magical 5 1/4 gallons of brew.
Since you ended up with 4 gallons and you're probably using a starter kit with a strain of forgiving ale yeast you will probably be fine. Take a final gravity reading when all the bubbles have stopped and the "head" (krausen) has completely settled. (1.5-2 weeks i'm guessing for your scenario). I'm guessing you'll want to be in the 1.010-1.020 range for the final gravity.
Regardless, you'll probably have some pretty good beer

Next time though, try the partial boil method if you are using a stove, or read around here about using a turkey fryer to boil 5+ gallons.