Well, if you have the booklets that came with the tractor, they usually have drawings in them that show the correct belt routings!
BUT!!
If you don't have the booklets, here's what to do. Run the front of the tractor up on a hill side, or onto some of those car ramps, or planks, to get the front up to where you can see under it. Now, with pencil and paper, try to sketch out the pattern for the belts, and how they go back on. Some careful sketching will be very informative at this point.
After you have the drawings made, release tension on the belts, and remove them. Clamping the clutch/brake pedal down will help immensely to get the main drive belt off and back on. But, you must remove the deck belt first, and reinstall it last.
Now, if this chore is more than you want to tackle, you'd probably be further ahead to have a mower shop do it! But---be prepared for a seemingly high bill for the work! (But, i know, if you aren't experienced in this work, you will probably rue the day that you tried to do it yourself! Ask me how i know this!)

skinut2234,
If you know the model # go to this web site put in the model # and select diagram to get a exploded view - ground drive and deck will get you both belts.
http://www3.sears.com/intro.shtml
Not so difficult if you take your time and have the tools, good luck?

OR...if you have a camera handy, take a picture and print it so you can use it as your guide installing the new belts!