89 mustang supercharged??

Good lord... Everybody starts somewhere, bro. Do some searching, look at some combinations, ask specific questions. Some companies offer kits with everything you'd need to supercharge your mustang. When you don't know a subject well enough to ask a specific question, it means you're probably not that serious, yet.
 
It Mainly depends on the engine your planning on useing.
How tired is it?
What has already been done?
If the engine is ok, then start from the block up, and get bigger everything.
Intake, Throttle body, Cold air, heads would be nice, mild cam, roller rockers 1.5/1.6/1.7 depending, headers, bigger fuel pump, and so on...
Then the electrical, you Should have gauges to watch things, advance controler, and more.
An intercooler would be a good idea to at least plan on, but not needed right away.

Basicly, a blower is a big job.
Your going from training wheels, to a jet car.
I have heard of people just slapping on the blower, but they normally end up breaking stuff after.
 
im planing on supercharging my stang with an extra 400hp what do i have to upgrade before i supercharge?

camshaft?
intake manifold?
fuel pump?

An extra 400 HP, so in addition to the 225 stock = 625? Everything needs changing then. The block, rotating assembly, entire fuel system, heads, cam, intake.
 
you will need a money tree in your backyard to start. once that is fully grown, you'll need:

-What platform you'd like to build off (302, 351, 408)

-Then, an aftermarket block (Dart, A4, R302, etc.)

-Rotating assembly (Crank, Rods, Pistons) keep in mind compression ratio

-probably somewhere from a 185cc head to a 205cc head (depends on cubes)

-intake

-then to tie the top end together, you should get a custom cam (Ed curtis, Jay Allen, etc)

-Exhaust...Probably 1 3/4" longtubes and a 3" exhaust system to go with it

-Don't forget about a transmission either...or suspension. all the power in the world won't matter if you can't put it to the ground

-Fuel system

-as for the blower, take your pick.

did i forget anything?