What to upgrade next
 

Here's my rig:
2001 Giant ATX850
17'' aluminum frame (2 inches too small)
standard wheels that come with a $1000 CDN bike
the same tyres that came with the bike
rock shox Jett XC fork (elastomer'ed, and doesn't work optimally)
Deore componentry
Worn out small and large chainring
bent derailler hanger
old derailler

May I ask:
What single (or two) improvements at low cost would make my bike faster during the race?

Drivetrain.

The only thing that needs improvement is the rider.
Wait 'til something breaks, then fix it.

Second that. I know people that can go faster then me on a department store bike. How cool is that? :D

A frame that fits?

There ain't no cheap upgrade on a bike with the problems you state, Drivetrain needs new parts, but Deore is OK ish. Not the best around, but works and is economic to replace. Worn chain rings will probably mean a new chain, and new rear sprocket aswell, so won't be cheap. A frame thats too small can be made to fit with long seat post and stem, but may affect handling, so thats the way to go initially, Jett forks are low end, but try a strip and rebuild to see if you can improve them. Wheels and tyres would be a definite improvement, but with the other problems you have, would be the last thing to upgrade.
Sorry but there is no cheap way on this one. New bike is what you are up for.

Good luck finding a rebuild kit for your Jett, I have an 01 Judy that I've been trying to find bushings for. Rockshox seems to have disowned their older forks.
I agree that the rider has the biggest potential for improvement. The components that have really helped me though are strong, predictable brakes and appropriate tires for the trail. Knowing that I can brake later going into a turn, without skidding, has helped me a lot. It's largely psychological, but that's definitely a big part of going fast.

It's better to have a too small frame then a too big one. I know. My 'boys' would agree with me.

:lol: Two resources
http://www.ekosport.com/ta_avlble_rsidx.shtml - Best bet
The second -try to find some MRP Speed Springs -they're no longer produced but someone's got a set on a shelf some where.

Those aren't exactly rebuild kits...what I'm talking about is like replacement bushings, seals, etc. Those are very hard to find for old Rockshox forks. The resources you've listed are to modify the fork. Thanks though