Already employed, how do I pay my tax on a one-off nixer?

Hello, I hope this is the correct forum. My problem is this, I already have a full time job, but I've always had an interest in web design. Now I have the opportunity to design a website for a company, in my spare time. It may be possible that if I do a good job, I'll get a couple of other chances to do some webdesign.

How do I pay tax on an irregular extra income like that?

Also, is it possible to be a freelance webdesigner, and set up as a very small company, while keeping my original job? I don't know if I could earn enough money as a webdesigner to survive without it.

Can't you simply enter such addtional non PAYE earnings in a [broken link removed] return if they are under €50K p.a.? Otherwise you will have to go on self assessment. That's my understanding anyway.

Thank you very much. I had been reading thought the Revenue site, but got very lost among all the jargon.

You would be entitled to deduct any expenses 'wholly and necessarily' incurred.. items such as 'civil service rates' would not apply, but any expenditure actually incurred is deductible/