First of all, it's great to hear that you have started to learn Python. I
can assure you that you are going to enjoy programming a lot more
with Python.
As Mr. Jha put above, it's never a hard requirement to use any particular
OS to contribute to Open source. In fact if you just give the source of
your college assignment problems (although, I would highly recommend
that you not do this unless you want your assignments copied by your
peers), you are already contributing to open source.
However, if you really want to try out open source OSes but are not
sure if you want to invest all the hard drive partitions, then I would
suggest you start off by using VirtualBox or VMWare and install your
favorite open source OS. That way you can check the OS out, see
if you like it, explore and play with it. Once you're comfortable with it,
you can go ahead and install it natively.
Regarding your question about GSoC, I have a bit of advice, please
bear with me, I am in the mood for some free advice right now and
unfortunately you have been trapped.
I would suggest you start contributing to open source projects with
the intention of learning programming, getting the experience of working
on a large project with developers across timezones, the experience
of working with a diverse team that is not co-located. GSoC, although it
seems like a really cool thing to have and of course the money is definitely
substantial, is not a great motivation in the long run. GSoC was started
with the intention of getting people hooked onto open source and not
as the end goal. In fact, most mentoring organizations look for students
who show the promise of continuing contribution to the project. This has
been my experience as well through GSoC as well. Please don't be
discouraged by what I said. There are so many GSoCers here and
almost all of them have gone ahead and mentored students, have been
regular contributors to their respective projects. Hell, some of them have
even been given commit access and have gone on to become the
highest contributors to the projects. In fact, I know of someone who
if I recall correctly, recently completed 2000 commits to his project.
That being said, I think right now is the perfect time for you to start.
Start looking for open source projects that interest you. Go on to their
IRC channels. Talk to people, go to their bug tracking system. Look for
little bugs with low severity/priority. Get your build environment set up
and hack away! In the next 5-6 months you will start understanding the
project well, your contributions will be appreciated. And then, you will
be in good shape to apply for GSoC.
Good luck and happy hacking! :)