wow thanks for all the great responses! i'm finally home from work and able to reply back...
i got the concept from these posts:
http://www.craftster.org/forum/index.php?topic=73848.0 and
http://www.craftster.org/forum/index.php?topic=67859.0 with more inspiration from the new CRAFT magazine's knitted boots article. but i suppose my way of doing it was different from all the others, so i made up some tutorial drawings to explain my methods.....
ok this is the way i made them. you can totally change things (like the shoe type, fabric type, etc) but i'm just telling you how mine were made. here it goes!
first, you'll need a pair of shoes that have rubber (or some material that you can staple into) around the bottoms, and that you can leave tied all the time and get your feet in and out. and then you'll need a big wool sweater - each side (front and back) needs to be at least wide enough to wrap all the way around the bottom of a shoe. i washed my wool sweater in the machine (cold, delicate cycle) to felt it just a bit, so it won't unravel at all, and that made it a little thicker/stiffer. (if you want to use a sweater that will unravel, just sew a hem on the top of each boot and it should be fine.)
so the front of the sweater will be one boot and the back will be the other, with the bottom of the sweater going along the bottoms of the boots. lay out the sweater, hold a shoe aligned with the bottom, and decide how high you want your boots to be. now cut off the bottom at that point.

cut between the front and back sections, and check how long the pieces need to be to fit around the shoes; cut off excess. now take one piece of sweater, fold it in half, inside out, hold your shoe over it, and sketch a line where you'll want to sew the boot, like this.

pin in place to keep the top and bottom lined up. now sew it up along the line, and cut off the leftover part.

turn it right side out, and pull it over the shoe to check the fit. you can turn it back and sew in closer at this point, if it needs adjusting. once this boot piece is perfect, try to recreate it exactly the same with the other piece. when they are both done, fit them over the shoes, and staple (yup, staple! with a normal stapler) around the bottom of the shoes.

it helped with mine that the bottom of the sweater naturally curled up, so the curling hides the staples. if the staples show and look bad, you could sew or glue a trim around the bottom to cover them up. or, you could try just gluing the sweater to the shoes instead of stapling.
ok i hope this helps you all, i've never really made a tutorial before. i'd love it if you'd post your creations so i can see other peoples' takes on the concept!