While poking around lookign for info on the 3000GT I found these two sites that have water injection kits/information

http://www.3sxperformance.com/alcoholinj.asp

This second site is in a screwy frame set up so click on the picture to the left that has "RTEC 3000GT TT" under it then scroll down some and on the left side will be a water injection install.

Clicking on the right photo will also take you to additional water injection info. Same stuff as in the first link but with prices in Euros to confuse you more.

Been there, done that. I built my own. It gained me almost 2 pounds of boost. The tank will be going back in come springtime. Don't need it in the winter. Plenty of cold-weather boost!