Legal milestone for open source

Question

Hi,

Some of you might of read:
http://news.bbc.co.uk/1/hi/technology/7561943.stm
"The court has now said conditions of an agreement called the Artistic Licence were enforceable under copyright law."

I'm creating a commercial piece of software with a small bit of code that isn't mine in it. I've modified this bit of code for a specific purpose.

Although the piece of code might seem insignificant in the grand scheme of the software I'm creating I've got a couple of questions. First is it OK that I am using someone else's code commercially? Second what would be the correct way to credit someone for the code?

Cheers,

Kevin