Both AMCAS (applying to MD schools) and AACOMAS (applying to DO schools) place their applications online somewhere in the late spring/early summer.
This means around May or June, barring no large technical difficulties.
I would have everything ready around that time, fill out the primary applications, and then send them off as soon as they are completed.
Have you taken the MCAT yet? If not, you can take it this spring (April 2002) or you can take it in the fall (October 2002?).
If you wait until Srping of 2003 to take the MCAT, your application may be delayed as much as a month.
Good luck.
JPH