Just create a connection in your Internet Explorer to 1892 150 150. this is the Eircom dial up number, its about 1 cent per minute off peak I think. Its what I use anyways.
You dont need a username or password or anything like that. It should work straight away.
stick with the dial up if it is going to be very light otherwise take a look at www.imagine.ie for the cheapest broadband here but they make u use their telephony services aswell but these are cheaper than eircom anyway