You're lucky, because I have a '96 Giant Iguana 950, which was the top of the line model only available in Taiwan at the time.
It's got a SR Duotrack 7005 fork with 20mm of travel, completel Shimano Acera X components, Weinmann something wheels, but I had to replace the rear wheel and hub because something was wrong with the internal stuff in the back, I have no idea
I'm very VERY pleased with this bike, because it's just so ridiculously durable it's not even funny. I take my bike everywhere, and I mean everywhere. Dirt jumping, light freeriding, trail, road, marathon, you name it. It's gone through tons and tons of abuse, and all the gears, cassettes, BB, derailleurs, crankset, not even one single problem, except I had to get the rear shifter rebuilt because a spring broke. I'm also quite surprised the fork isn't dead yet either, considering I bottom out every bump I go over...
Anywho, I wouldn't spend over $200 on my bike right now, on reason, because it's a waste of money to be upgrading something so old anyway, and secondly I'm buying an actual DJ bike soon.
If you really want to do serious trail riding, and not get a new bike, I suggest you get a new fork (threadless), which would also require you to get a new headset, stem, handlebar etc. (Also, not 100% sure on what upgrades are actually needed). That's what I plan on doing with mine, buy a fork off pinkbike or craigslist, a cheap RST Capa 80mm or Suntour XCM/XCT 80mm, which you can easily buy for under $100. The extra stuff shouldn't be too expensive, unless of course you buy new parts.
I dunno, it's up to you, but as I mentioned, I'm getting a DJ bike, but I plan on keeping my Iguana, but all it really needs is a new fork, because I don't think my current one can take much more abuse
Here's the specs for your bike, it might come in handy
http://www.bikepedia.com/quickbike/...996&Brand=Giant&Model=Iguana+650+SE&Type=bike
All the upgrades I have on my bike right now are green Steve Hamilton Animal Plastic Pedals, and Oury green grips (because my old ones were ripped).