We have used products in the past from Vaistech:
Video,Audio Information Solutions for Toyota and Lexus (iPod integration,XM and Sirius SAT radio integration,MP3 integration,Auxiliary input)
This SLI unit is what we have generally installed on Lexus vehicles with no problems. However, call tech support at Phone: 720-733-2348 because we have only used it on later model Lexus (post 2001). If it is not the same and they don't make a unit for it, you could try Peripheral by AAMP or Axxces by Metra. We are a Peripheral authorized distributor but we only stock their late model iPod/HD radio integration units at this time. Their website is:
Peripheral Electronics
I don't see a listing for your vehicle however. Post your results of what you come up with anyway for others looking for that answer please!