Using Open Source software to make a product to sell

I have looked over a few posts in this forum and tried reading up on things like GPL, but I'm so confused with all the jargon and stuff, so wonder if someone could clear it up for me please.

Say I took an open-source CMS like Mambo for example, and then played around with a few things, maybe add a few features to get it to do what I want, would I then be able to sell that package on to make money for myself?

For example, take sports clubs... could I get the CMS and add features to make it suit a sports club, then for each sports club as my "client" just change the templates and CSS and then sell it on? How do I stand using the software that is open source in that fashion? It's like making profit for someone else's hard work.

Thank you in advance.

Andy

That's a good question. I'm surprised no one has commented on it. With all the open source software out there, you would think that you can make a monetary killing. But if that's the case, why aren't more people doing it?

Hope someone with experience can answer this question.

It is my understanding that you can as long as you give your customers your source code under the GPL so they can do the same.

This is possible, but it depends how you are selling it...

Its easy to sell these things as 'components' of the main CMS, Although it may look technical to end user but you have to maintain presentation as well...