O'k.. i'm wanting to put new exhaust on my sidekick but i mite as well put a header on it before i have the exhaust done.my question's is what's a decent header to install? is the shorter header better then the long tube header? And is the performance timing key worth installing as well.It's my daily driver so i'm looking at what's best for me.

Go with a Thorley header.

The timing key will lower the RPM where the power band starts and stops. ie, you will see a lower topend whp#'s but below that in the midrange and bottom end you will see some gains in torque/whp numbers and performance.

I went with the Calimini header for my 16v because it was a direct factory replacement, just bolted straight in.  Works great, didn't require any modification of my existing exhaust and kept the 02 sensor in the stock position.  Then I went with an aftermarket 2" exhaust, I should have gone with the heavier duty muffler as this one is starting to see wear after 3 years.

I've used the Calmini header in the past and found it to be of good quality and it did help performance with a K+N air filter, full 2" exhaust with a freer flowing turbo type muffler. I would only change the timing key if your willing to loose your top end. JMO.

The Thorley header is a TR-Y design witch is better for lower RPM' add the crank key for more torque .more lw end torque = better drivability.

The Thorley 16 Valve Ceramic Coated header is only $250.00. I thought that was a descent price.I cant tell from the picture but is the o2 hole in the flange or does it just read one cylinder? My other question is my suzuki is 98 and my second o2 is after the catalytic converter.So can i take it out or will it confuse the computer and if so what can i do or is there an after market converter i can put in it's place?

On the Thorley it reads off of two cylinders instead of 4.  But the mixture should be pretty much the same.  One item of note is that the Thorley is not California certified, if that is important to you.

The secondary 02 can be faked with a resistor but I don't have the number off hand.  I would recommend running a cat if you can, a free-flow cat won't change your performance much and it is better for the environment if you have a DD.  On a trail only rig I can see bypassing it but for something you drive every day it is worth it to pony up if you can.

If you want a little more top end at the expense of a little bottom end you can of course put the timing key in the other way.

Were i live in oregon we don't have smog law   So am i better to use a stock or free flow catalytic converter? Yes this is my dd.

I would use a freeflow cat and the down stream o2 sensor . If the o2 sensor/and or the cat are not there it will trip the check engine light and set a code. Unless Want to flash a prom, and I don't know if there is support for these trucklets, may not exist ?
Try Quantum 9,  they are in Oregon and supply exhaust parts to small repair shops.

The secondary o2 sensor is only there to determine if the cat is functioning correctly.

The secondary o2 sensor can be tricked into reporting to the ECU that a functional cat is installed when the cat has been removed with a pair of spark plug defoulers that are configured to stand off the o2 sensor from the main exhaust flow, thusly creating a partial vacuum around the sensor that is devoid of oxygen.

legal disclaimer:::: this is for offroad use only..................................