unless you are mechanically inclined, i wouldn't attempt it. automotive springs can be VERY dangerous if it's not done properly (a flying spring can rip off an arm and fingers like it was a hot knife through butter).
if you do attempt it...make SURE you use a spring compressor. do NOT attempt to install springs w/out one (for the above arm/fingers reason).
that said, there are plenty of install guides on the web, i beleive either Turbo magazine or import tuer also has an install guide for the 7th gen celica..check their website for the link