Designing a simple app for OSX, what to use?

Hi everyone, just signed up, seems like a great forum!

Heres my problem, I'm web developer and I have a web based script(PHP/CURL/HTML/JS) that gets latest threads from forums with job listings, however right now I have it email me when a new one is made, what I'd like to have is some sort of an app, basic idea would be a browser type app, where it would load in the url, and then html/css would do the rest, refresh every X seconds, play sound if there is a new thread, etc. (however I don't want to just have a tab open, I'd liek it to be a seperate app, I know this is rather easy in VB on windows)

What language would this be coded in and does anyone have any starting points? I have basic experience in VB, but thats about it as far as programming software languages.

Eventually I'd like to make this into an API with the program requesting XML from server and then style it from there, as well as functions such as contact the thread poster etc(but this will require a lot more experience from my end in order to design the functions that could call to the server with all of the parameters etc)

Any ideas would be appreciated!