What turbo kit are you looking for or are interested in? There are numerous kits available for your SI. Greddy makes a nice kit so does DRAG and MaxRev. You can check out everything on the site @ www.hpautoworks.com
drag kits are alright, except for their wastegate placement..thats not optimal. greddy comes with a internally wastegated turbo, which is NOT t3/t4 compatable. so if you plan on upgrading in the future do NOT go with that kit, youll need a new manifold and new dp. id say go with a homemade custom set up. or posible (if you got the cash) go with the www.fullrace.com turbo set up..