Dunno if you're going to like this answer, but our cars don't have much support from the aftermarket companies like an Eclipse or Civic would. That said most of the stuff you do to your car will be custom. Stock psi from the turbo is ~7psi, you're limited to about 8 or 9 because the popoff valve will vent off excess boost unless you cap it or shim it to accept more boost. Stock block is rumored to be able to handle 300hp or so.
Turbo upgrades... You can get a T3/T4 hybrid, umm, I think Crane cams makes a cam for the Z or maybe it was Crower... If you check out MSA they have a whole kit for it. HKS makes a few parts for the Z and Trust/Greddy does too. That's about it, 280zx Fever hit the bov on the head, so all you have to do is decide on what sound you want and you're good to go.
John 82ZXT

 

I haven't done the shimming/capping thing, I got lucky and found an HKS adjustable one for cheap. However, here's a link for the popoff valve modification. If you don't want to go through that, you can go to Home Depot and buy a 1" pipe plug and plug that thing off.

popoff valve mod

You'll need a pretty big crescent wrench to get that thing off.
John 82ZXT

 

I went to my local hardware store and in the screen door section found some 1" diameter compression springs. Of course they were about 6" long so I had to cut them. My Popoff valve pops at about 26 lbs of boost now.
Before you go cranking up the boost, you have to install an intercooler! There is no way around it unless you just want to watch your ZX blow a hole in itself for the fun of it. Check out eBay for intercoolers and the classifieds on this site and others. You might find someone has a whole set for sale, I did. Installing the intercooler is pretty easy, although you will probably have to do some cutting in your radiator support.
After you do all this you can run about 12-15 lbs boost and still keep your air/fuel ratio in the stoichiometric range. If you want to go higher than that, you will have to do some fuel system upgrades, but for the gain in horsepower, it is well worth it in my opinion.
If you check out my gallery you can see some pictures of my intercooler system. They are not real detailed but they might help.
-Kel

 

hey lifegrddude, when you say the block is good to 300hp, are you talking about the block itself or the entire bottom end. I'm still adjusting to cars that need more than forged pistons to run 300+ hp (one good thing about the isuzu was the bottom end was tough as nails).

 

I was referring more to the pistons and con rods. The pistons are usually the first things to go on a turbo Z. The stock bottom end is pretty tough. I haven't pushed anywhere near 300 to the wheels yet, but when I do, we'll see what gives out first! I've just got to get a hold of two more 370cc injectors and a fuel pump and I'll be ready to try my luck at cranking up the boost some more.
John 82ZXT