Kirk is a Scottish word for "church", generically speaking, but now it is used (often with a capital K) to refer to the Church of Scotland as an institution. I say "now" but I expect that's been the case since the Reformation, when a distinction first needed to be made. The mainland Church of Scotland is a laid-back, Protestant, Presbyterian Church - it has women ministers, and I'm fairly sure its clergy perform same-sex civil unions. They are much more "staunch" in the Highlands and islands, though. There was an uproar about ferries operating on the Sabbath, which pretty much sums up the difference.
"Does he go to kirk or chapel?" used to be a way of asking if someone was Catholic or Protestant, but in this secular age, it's outdated. Nobody asks because frankly, these days very few people go to either. My dad's family is Catholic, however, and my grandmother would not appreciate a great-grandson named Kirk! (She's practising, and of a generation that feels it is important.) None of this ought to bother you since you're clearly not in Scotland :-)
About the surname ... I expect it just denoted someone who lived near a church, originally. No it isn't an established in first name in Scotland. Many surnames as first names are primarily American in usage, and Kirk is just another of them.
I thought Colleen was originally taken up by Irish immigrants - or their descendants - in countries such as America and Australia. I don't think it has significant usage in Ireland.
Edited: I cannot spell today!
This message was edited by the author on March 22, 2007 at 8:52:26 AM