Is it possible to get tickets for a tour to Newgrange over the internet for a certain day and time?

This is a continuation of my question-I do not want to take a tour from Dublin but go on my own. I would take the Newgrange tour when I get to the sight.

I do not believe you caqn pre-purchase tickets anywhere BUT at the visitor's centre itself.

We took Mary Gibbon's tour and even she took care of the ticketing when we arrived. I know that there is also a shuttle that you can take from Dublin, but all tix are purchased AT the centre. I know that you don't want to take a tour but I think that the only people that guarentee intro. is Mary Gibbons and I believe the other is called Over the Top Tours.

If you purchase your Heritage Card before hand (or even there if that is the first site you visit) it will gain you entry but you still have to wait. Once you get your tickets you are set for a particular shuttle from the centre to the site and you can meander around and check out the video, gift shop, museum and wait for your time.
Good luck!

here's the heritage ireland website:
http://www.heritageireland.ie/en/His...angeandKnowth/

If I drive there it would be the week-end of Easter (Sunday). Do you think it will be very crowded? How long a wait?

Yes, it is likely to be very busy.

It can happen that visitors do not get to visit the chamber. Capacity is limited. You might be offered a visit to Knowth tumulus instead; it's worth seeing.