Registering in Poland for a NIP tax number?

Hi just a quick question,
So I have recently moved to Poznan and found a bit of work (very small, one day a week).
Anyway my employers told me that I need a NIP tax number.
I started looking into registering today and found out what I need to do. I went to the citizens and foreign department (or something like that) and I have to fill out a form and send it with a copy of my passport and job contract, wait 2 weeks for the reply then take that to another place to register a temporary stay of more than 3 months.

So I have a few questions.
Is all this necessary for a few hours work?
What does registering in another country do to my situation in my home country (Ireland)? When I go back do I have to register in Ireland?

Any help much appreciated.

I was given a PESEL number so I can take out contracts for insurance, mobile phone etc

I am classed as permanently living in UK but temporarily living in Poland for the next 5 years.
There is no affect on you living back in Ireland.

Thanks for the reply Steve, oh right I was told that I didn't need a PESEL just a tax number?

What kind of work are you looking for here?

Teaching English

It's a tough, tough market right now - the work has dried up considerably here in Poznan, and there's more and more natives arriving and looking for work.

If you want, I'd be happy to meet up for a beer and a chat about the place - maybe I can help a bit? :)

It used to be that you needed a NIP for working and PESEL for credit or other stuff. But now it has become a case of one or the other. If you have a PESEL now, you don't need a NIP.

Yes, exactly. You need NIP only if you run your own business. If you are employee - you use PESEL for tax issues.

Okay brilliant, thanks everyone.
On my contract they told me to put my passport number where it says PESEL and that I would need the NIP.