does anyone know how to apply for a btopenworld job , thanks in advance

All BT jobs are advertised on bt.com/careers.

do you know if they are a company worth working for

It depends entirely on what part of the business you want to join and on your job role. I work for Openreach and they're the best company I've worked for but I can't comment on BT Retail, Wholesale or any other line of business as I have had no experience with them.
The benefits are the best I've had too.

i worked for sky previously and they were pretty poor, i dont want to repeat that experience , ive spoken to a few openreach engineers and they seem to like it

I worked for BT Retail 150 customer service for around 5 years then moved over to Openreach as an engineer for the last two, you will never find everyone 100% happy all the time in any job, I really do enjoy working for BT though, the money wasn't great to start with.

BT/openreach do their engineering recruitment through :

http://www.hays.com/jobs/bt/
HTH

they also recruit via totalstaffing.co.uk good luck .