Not done this myself but would like to take a peek and a programmer myself too. I think you need to look at NodeJS, C/Java server or something else that handles websockets well for the live connection. You can do it in PHP with a websocket library if necessary I believe but may have sociability issues if you're going to make this a service for others to use too.
These would be the three steps I'd do...
First step - get a websocket system that follows share price via mtgox or other API that supports this websocket system.
Second - Test your algorithm on buy/sell requests based on test data
Third - Call into the buy/sell API such as Mtgox, Bitstamp, bitcoin24 etc..
Probably not that difficult but will take a lot of time and a lot of testing especially for scenarios when DOS attacks causing panic selling happens. At the end of the day it's still gambling on random odds, you'll probably find you'll lose money via an automated system unless you have options for short selling, market influencing, using someone else's money or other tricks the bigboys use in the city's trades.
You may find it's easier however to just use something like bitcoin-bot.com that's already out there for safer and smaller scale automated trading though
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