Gentoo is a really good distribution at the price of the ease of use. I'd probably go with something like Ubuntu, where it has had a lot of media in comparison to other flavours and probably more documentation. As for getting Ubuntu, you can get it off the website (download through normal web HTTP or use bittorrent) or you can order some free CDs for it. Do know that ordering the free CDs isn't a scam or anything, it does take nearly 6 weeks for you to receive them though.
As for dual-booting, the easiest way is to probably use the program Partition Magic - mind you, it does cost quite a bit of money for something you won't use daily. Anyhow, I recommend that you don't pay and use the free alternative - Qtparted. You can use Qtparted by downloading the Knoppix Live CD - it has that and many other programs on it.
Good luck, just ask around here if you have any more questions.
I don't know, Gentoo still seems too hard for me, whether it be to learn or to use. I have heard that customisation is an area that Gentoo really excels itself in, however, I think I might stick with something less ... advanced ? Right now, I'm just playing around with Kubuntu after being bored in the holidays. This time is going alright now, better than the disasters that occured the previous 6 or so times I've tried Linux.
i am using ubuntu on this laptop that I am browsing from and its AMAZING!!!!!!! I love it and soon i plan on transferring my desktop pc to ubuntu as well (cause bf2 is being more and more better supported)