There are two parts to this question:
(1) How can I detect URLs in a given text?
(2) How can I make clickable a part of the text in a text field cell (in a table view)? I would like URLs, when clicked upon, to open in the default web browser.
For making URLs clickable please take a look at this guide from Apple: Embedding Hyperlinks in NSTextField and NSTextView
For the first part, are you married to using an NSTextField? The reason is that NSTextView provides this automatically (it is just a checkbox in IB). Otherwise, have a look at this answer on StackOverflow regarding the Latent Semantic Mapping Framework.
I have not used it so I am afraid that I cannot offer any suggestions on it.