here you go, sry ad work the last few days.. could not answer.
Super heavy class resistance bands

www.amazon.com/Harbinger-Super-Heavy-Res...287253537&sr=8-1

I use these

http://www.ironwoodyfitness.com/fitness-bands.php

They wrap around the bar and you can play your foot or knee into them.

They are a little pricey but I went from doing zero pullups to repping 8-9 now. Each band offers a different amount of assistance. First month I used the black band (100 lbs) second month I used the Green Band (40-60 lbs) and the third month I used the blue band (25-30 lbs). I am still using the green and blue bands now that I am in round 2. I will do unassisted until failure then use one of those bands depending on how i feel.

A tip I pick up from Men's Health is to do Negative Pull Ups. Basically start at the top and lower your self slowly.

If you notice weak points on the way down, try to pause 2-3 seconds just above these points on the next rep.

Per their advice, if you can control the negative move, top to bottom, for 30 seconds, you probably now have the strength to complete 1 standard pull up.

6 months ago, then I was working out at the gym (before shoulder injury) I could do 15 wide pull-ups... At the moment, I'm on second week of P90X workout and I can only do 6 wide pull-ups. First week it was only 3.

I just know from the past, that you have to do as many as you can with your own bodyweight and then add the chair. Write it down like this: 7 (15), so you will know how many you did on your own and assisting chair.

Also, I had a rule then I could do 15 pull-ups: whenever I passed the door where was my pull-up bar I had to do pull-ups. And it was my bathroom, so every time i had a piss, I had to do pull-ups, it helped me a lot!

You gonna see progress shortly, trust me.

Just keep pushing yourself!

Pullups are great! They are listed as a 'back' exercise but will really expose weaknesses in everything from your grip strength, forearms, biceps, triceps, shoulders, back and even your core. For me my personal weakness seemed to stem mostly from my shoulders. This is exactly why P90X is great -- you spend the weak working on every one of those elements and over time you see your progress in your pullups!

As many have stated before me, do as many as you can unassisted, then switch to whatever assisted method works best for you (chair, bands, negatives, etc). I think most have found the greatest improvement through integration of negatives vs. chair/bands, but do your best and forget the rest.

Once you can do two or three unassisted, if you really want to improve quickly, there are dedicated pullup programs out there with daily and weekly cycles to get make significant gains.

Rick