i have windows XP at the moment, and i feel like experimenting with Linux.
i will most likely keep both windows and linux on the hard drive. but if later on i decide to want to wipe windows and just have linux can i then later put windows back on if i have the original windows disk?
and which linux is the best for a beginner? Ubuntu?
If you have an original XP disk and the appropriate key you can always reinstall Windows at any time.
Best Distributions for a beginner seem to be Ubuntu, Fedora, or Mandriva (in no particular order). You might like to get hold of some Live CDs and try each of them out to see which works best on your system and which you prefer. Bear in mind that a Live CD won't run as fast as a proper install, but it's a good way to try things out without committing yourself.
Make sure you have a backup of all your data first, and it helps to also have the XP disk and key if you need to reinstall, as ijack said.
From experience, the 4 best ones are Ubuntu, Sabayon, Linux Mint and PCLinuxOS. Ubuntu is the most widely used and community-supported, and Mint is Ubuntu with a fancy makeover, so I would aim for one of those two for starters. I like Sabayon and PCLinuxOS as well, but I point to Ubuntu for beginners.
I see so many people saying Fedora and Mandriva are one of the best, yet EVERY machine I have put Mandriva on runs slow as molasses in January in Fairbanks and Fedora is more suited for a business rather than a fully-featured desktop. This is just one fellow's opinion.
Best advice is to get a few on LiveCD's and test them out. See which one works best for you and which one you like overall.