Mountain Biking - My bike, some questions

Hi, I have had this mountain bike for sometime, I have just used it for commuting to and from school, etc.
its a Giant Iguana SE, see pic:
http://img508.imageshack.us/img508/5073/img6183pk5.jpg
I dont remember when I bought it, I want to say back in spring of 2003.

this summer I am looking to try out some more serious mountain biking and maybe start some races.

I am a pretty seriously road racer who knows literally nothing about mountain bikes.
my question is, what do I need to upgrade on the bike to make it more trail worthy.
pedals/shoes are a given, i also understand that v-brakes are out of vogue.
On a stock bike like this, what are some of the first places that are usually upgraded, etc?

any tips are appreciated,
thanks

If it were mine I'd just ride it as is. Replace anything that's broken or worn out and ride.

Is that seat comfortable? Looks pretty angled up...

Yeah, pedals, shoes, maybe change to a saddle you really are comfortable on. As far as the V-brakes go, V's are certainly trail-worthy and adequate for racing. For disc brakes, it appears the fork is set up for them but your frame is not. There IS apparently adapters for retrofitting discs in the rear, but i don't think many folks use them, nor do I have any experience with them. I would suggest that you go with the bike set up basically the way it is and get some riding time in, read this forum along the way to educate yourself, and things will naturally become apparent to you. If you end up enjoying riding MTB, you'll probably end up like most and start looking at new bikes with all the new stuff on 'em, perhaps even full-suspension. :D

Thanks for the quick replies.
about the saddle, definately going to be putting on a new one, the same i use on the road.