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I'm no guru, but here we go...
Q: Which Linux distribution shall I install?
There's a whole bunch of good ones. Check out
distrowatch.com. You mentioned Red Hat, which is my favorite. SuSe is also great. If this is a test box check out Fedora. For business you'll want something more stable. Use the latest stable version of what ever distro you choose, especially for your first time.
Q: What software can I use for windows emulation (my best guess is wine)?
Winblows emulation? Yuck! There's plenty of great apps for Linux. Wine doesn't work half the time and it's slow. I never use it. There's others, but again, yuck.
Q: Which boot-manager can I use, when installing win XP in parallel and going for dual boot?
Grub. Dual booting with Red Hat / Fedora is (usually) painless. Install Winblows first. Then Linux. Most of the magic happens on it's own.
Hope that helps some. If you're going to play in the land of the penguins you should consider joining a local
linux user group. They help me a lot. Good luck!