mmmmmmmmmmmm....
As already said, speak to JGM.
Power Enginnering used to do a daughter board addition for the 98 ecu, but i dont think its available anymore. It was only a "crude" remap anyway. I believe Andy at ESL is also working on a solution for the 98 car.
Best bet is to go for a Simtek, or Apexi,Gems, Motec, or solaris, depending on your Mods.
Simtek would get my vote for good value for money with the addition of some nice "add ons" if you wanted them!
Good Luck
jon