Once you have decided to take on one or more employees, then - as Claire says - the next decision is whether or not you pay someone to take care of it for you. That has to be a balance of cost to you (what they charge) vs what you "save" in terms of time/hassle/"am i doing it right?" uncertainty (they have to pay for the software & keep up to date with changes etc). In addition, sometimes an additional pair of eyes can spot things you might not etc. It might be someone "in house" (your book-keeper) or it might be external.
If you are in business, then (just like book-keeping) you may find that your accountant will either be able to provide a payroll service, or be able to recommend someone.
If you choose to run the payroll yourself, you then have to decide how. In The Old Days you could quite easily run it manually; but these days the requirement to submit things electronically means that software is essential. I believe you can still keep the details manually, and use the Revenue website to submit forms; but I have never done that so can't comment on that option. No doubt others will be able to advise you.
In terms of software (& not forgetting related stationery), yes Sage are well-known; but there are many other systems out there, each doing the same job but each having their own strengths & weaknesses. We have some clients who use Sage; others use Pegasus. Both are well-established and well-used. An increasing number choose Moneysoft though ( http://www.moneysoft.co.uk/payroll-soft ... anager.htm
) as a simple-to-use, no frills option that is reasonably priced and does the job. For a small payroll, it's a good way to start (& they have a very good helpline too).