> I hope to use example  code or samples  to base  my
> programs on. Can I redistibute these modified
> code  as my own? How much do I have to modify  free
> code until it becomes my own? Can I use this commercially?

There are legal issues with this, and I am not a lawyer. You can modify
free code ... however it doesn't become your code untill it is all
essentially yours. If there is still code in there from other people,
then they still need to be refferenced too.

> Links to sites  plus some info  would be nice: does "Open Source"
> mean I can do the above?

Commercially, that depends on the licence they are published on. With
most generic open  Source things, you can create commerical products that
stand along side with open source prouducts, but you couldn't claim that
open source product to be your own as well.

> I hope to share  my examples  with other people and the group  and post
> examples on the Internet : I do not want any copyright problems.

The tricky problem when you want to commericalise code is making sure
that every single person who contributed to a product is reffered to and
rewarded for their time, and they allow their code to be used.

Essentialy it comes down to a point, imagine how annoyed you would be if
someone was making money off of your code, and you made nothing.