"If I get a mac will I get any problems If I start to use programs on it?"
Well they use their own programs, not exactly the same ones on Windows. But there's always an equivalent, and lots of good freeware.
"Also can you get them with firwire etc? "
Apple invented Firewire, so all their computers work very well with it. MacBook Pro has FW800, the faster standard, as well as regular firewire (400).
"Are they easy to pick up?"
Given that you're going to be writing code for a website, so presumably know more than Joe Average about computers, yes, very easy. And there are many, many great forums to ask questions in.
If you do a Google search for images of corporate HQ offices of some well-known web-based brands, like Yahoo!, Flickr, Delicious, Google, etc., then you'll find lots and lots of Macs. There's a reason for this. They're really great machines for doing web-based work.