Intel International Science fair

a science fair sponsored by intel
im going to enter under computer science and build a phase change system and overclock my brand new 8400 c2d
any ideas on what i can do with the oced proc like algorithms or some thing like that with code i can write myself
and of course ocforums will be my sponsor

Good luck, read the guides.
Intel PR asked me for a unit about a year ago for something similar.
Chances are unless you build a 3 stage system (take you years n years) you won't be anywhere on the ranks.

have people even built phase change for this in past years

I've never seen this contest but SS phase is so mainstream, its lost is ooooh factor.

what do yall think about a auto cascade or ln2 and dice
i believe all of you underestimate me lol i am a 16 yo high school student
i am taking physics and chem. the only thing i lack is the tools i understand the concepts the only thing i would not do is fill it
i need a little nifty diagram for a 2 or three stage system
i am talking ti kIngpIn about ln2 dice and evaporators

You'd really need a nice three stager or an autocascade to really be "oohh" and "ahh". Cascades are much easier but an autocascade shows more understand and takes more effort. That being said both can be incredibly dangerous and involve a lot of risk in construction without the proper techniques.

thats what im worried they could turn it down be cause of so much pressure
isnt a autocascade just like two refrigerants in one

What's your time period for getting this operational? By asking that question.. you need many months of studying and practice building other units before considering an autocascade. At it's heart an autocascade is indeed a single compressor with multiple refrigerants however it separates them out and uses lower pressure refrigerants to condense higher pressure refrigerants to drastically lower it's evaporator temperature versus a single refrigerant system. It isn't even this clear cut though, autocascades are all about mixing of gases, mixed state stages, and a lot of trial and error.

you give me a schematic i can build it the only thing i would send it off to do is to fill it and for somebody to tune it i have till march of like 09 but i am going to use a single stage and ln2 for the qualifying round near me its like in dec.

Sorry, but no can do. I will however point you into the direction of the best guide available from Michael at XS.
http://www.xtremesystems.org/forums/showthread.php?t=144007
Finding somebody to charge an autocascade would be very hard.. not many people stock the entire slew of gases you'd need to have an impressive autocascade. Your best bet would be a butane, ethane, ethylene charge which is cheap to acquire, maybe $300 in gases if you can manage to buy in 1 pound increments. Then add on regulators and you are looking at $400 or so just to charge the thing. That'll net you with the gases to hit -90C or so unloaded. If you can manage an argon sub-cooler then you can dip into the triple digits at the cost of capacity. Read through that thread and then decide if you want to travel down that road. If so then build a single-stage first and be successful at it before deciding to build something that could potentially kill you.

The easiest thing to build by far would be a 2 stage cascade, your bread and butter R507/R1150 cascade. Use some decent sized(3/4hp) compressors and you'll hit -110C unloaded and ~-95C loaded.

would yall be interested in selling me used compressors cus the ones i found online are pretty expensive i can get condensors and i have a metal lathe so i can make a evap.

Ebay will be your friend.