I have this product hooked up to my stock stereo (2000 Trooper). You MUST keep your stock CD changer to use it, though:

http://www.pie.net/index-2-details.cfm?recordID=X3-TOY

The other option is this:

http://www.pie.net/index-2-details.cfm?recordID=TOY-AUX

You MUST remove the CD-Changer to use this one.


There is also:
http://www.logjamelectronics.com/soundauxtoy1.html

and a whole assortment here, many of which should work if you choose the 98-02 option for Toyota.

http://www.logjamelectronics.com/auxtoy.html

Nate