NB: There are a handful of replacements for MACs;
Oh and tip: If it's anything like the Windows version, LibreOffice is nothing like Office, unless having a word processor, spreadsheet etc counts as being "Just like MS Office" (and I'm sorry but in my world, it just doesn't, it takes more than that (and nope, not referring to the god awful ribbon, bloating, social network integration, it would actually be more like it if it had those things too (though LibreOffice did seem guilty of being a resource hog when I last tested it)))
MAC users will likely know quite a few more potential replacements, just be as wary of their forums as you would be a Linux forum - they're not exactly known for being kind to newcomers (or for that matter, those that simply have a different viewpoint than they do (does make for interesting and very cheerful reading though)).
Windows XP users however, do at least have another 12 months to upgrade (I'd recommend Windows 7 over 8 personally)
* Unless you're a fan of "Microsoft bashing", you'll not want to bother with the comments on the article on theregister.co.uk - sadly, articles even remotely mentioning Microsoft, even if indirectly, always results in a flood of anti-Microsoft comments, and rarely anything but that (there are still alot of great commenters on El Reg though, but amongst the floods, they're sadly, few))