I haven't visited the STS site, but I can tell you people have swapped in the 2ZZ, several Toyota V-6 incarnations, supercharged and turbocharged the Spyder. A turbo kit can be found here (disclaimer, I do not work for them, and have no experience if this is a good product or not):
MWR Turbo Kit - GT28XX - Toyota MR2 Spyder 2000-05 - MWR-5051X5 van Monkeywrench Racing -
I went to their (STS) site - turbos added on as they do apply primarily to front engine vehicles already tight on space. There is an increased amount of turbo lag encountered just to save the cost of an exhaust manifold. Not a good proposition IMO.