Zonker on Open Source licenses ..

[Doug Mentohl]

If you're altering for internal use only, typically there's no 
requirement to do anything. If you alter the software and redistribute, 
then it depends on the license whether you need to make changes 
available or not, how you need to acknowledge the original software, and 
so forth ..

There's also the matter of the so-called 'viral' nature of the GPL, 
which means that if you incorporate GPLed software into your product, 
you may need to distribute the entire thing -- not just the original 
GPLed product ..

Note that mere aggregation doesn't mean you have to GPL the entire 
thing. So, for instance, if you have a program that does its own thing 
distributed with a bunch of other software, that doesn't mean all the 
other software has to be GPLed. But, if it's 'derived' from the GPLed 
software, then you need to GPL the entire lot.

http://www.daniweb.com/blogs/entry4065.html