Hi Jprao (I'm glad I don't have to try pronouncing that),

Look for USB to UART bridge chips. Silabs makes one that I use, but I'm sure there must be others. The Silabs CP2102 will replace your max232 level shifter, and comes with the drivers you'll need for interfacing. I suspect others work about the same. The bottom line is that this is as close to a painless transition as you are going to make, from UART to USB. And it really is pretty close to painless. There's no need to do any circuit redesign.

If, on the other hand, you've got it in your mind to "roll your own," then find a copy of John Hyde's "USB Design By Example; A Practical Guide to Building I/O Devices" (ISBN 0970284659). You won't want to "roll your own" for very long.

Joe