i got a 97 gst and just recently it started to blow smoke out from my tail pipe i had it checked and mechanic told me to change pcv valve and valve cover gasket ...but wen i went to tighten the pcv valve i cracked the valve cover so i stopped ..i also checked the sparkplugs and had oil in the first slot... i was told it could be he piston rings..if anyone has anything different or the same problem im all ears...

 

All and any of those sound correct. You probably have a bad head gasket. Possbily even a cracked head.

 

Start small. It may be the head gasket. It may be just the valve stem seals. I would pull the head. Buy an upper engine gasket kit. Have a shop do the head. Then put it back together with the new head gasket. If you are close to the time to replace the timing belt, you might as well do that. If you do this, it will probably cost about $200. If you have a shop do it all... $500 to $600.

 

According to the paperwork on my TSi, its about $575 (Inc. timing belt) of course that was in TPA.

 

PCV slot...that needs to be brazed. I've cracked mine too. I used a gasket maker to close the hairline crack, lol. No worries though because I've got 2 spares. These thin aluminum valve covers don't need 20ft lbs of torque, you really have to be careful with them. Anyway, braze it or swap it out.
Smoking tailpipe..what color, how thick?

Leaky spark plug tube seals (oil in plug chamber). You need to change out the spark plug tube seals. They are most likely hard as plastic instead of soft like rubber.
You'll need to replace the valve cover gasket and tube seals all at once....why not, you'll have to remove the valve cover to get to the tube seals anyway and why would you? Besides, you've got a leaky seal, it will have to be replaced anyway or you will go through a bunch of plug wires. You'll have misfires, bad idle, etc.

Since you're new....welcome to MF btw...and since we have no clue on what you have modified, I'll start small. The head gasket change is too early to jump into with just a "smoking tailpipe" comment, IMO. There are a few other things that can cause that too, not to mention, he never stated the color of the smoke or if he has oil/coolant mixing or fluids leaking down his block. All of those are indicators too and should be added or noted somewhere

Need more info on the smoke bud, otherwise a simple thing can become a motor rebuild.