I'm dual-booting winxp and ubuntu, if I were you, I'll just upgrade to windows 7, 8, 8.1 or linux mint. The only problem is that there is not much software that supports mint or ubuntu and the wine emulator can't run all windows software (e.g, chrome).
If you walk into an OS transition with the requirement that you want to run Windows based software, you're either not a good candidate for a Linux transition or simply not looking at the broader scope. There are some instances where Windows truly needs to be in place, but that gate has been closing more and more over the years. We've transitioned our entire infrastructure (several thousand systems) to Linux with extremely few issues, especially in the application department. My experience does NOT constitute 100% of the situations out there, though.
You can handle this in a few different ways. Some country (Germany?) recently underwent an entire Linux switch. They first started by finding open source alternative applications that are available on Windows and Linux. Over the years, they began to get their users accustomed to this software, such as Libre Office in place of MS Office, etc. Once that was done, they swapped the underlying OS in a hot second without issue. Since XP still has some supported life left, you could do that. Switch the user in question over to some open source alternatives available on both platforms and see how it goes. If the transition goes with minimal fuss, you're literally 95% already there.
Afterwards you'd be looking at switching the distro, and different distros come with different desktop environments, or interfaces if you will. I personally wouldn't use Ubuntu. Lately Canonical has been making some questionable decisions, but even when you remove the politics from the situation, Ubuntu's Unity desktop environment is still a fat pig and quite resource intensive on even semi modern day hardware. I'd get yourself exposed to a few different distros and environments first. After all, you can't help train on things you don't know, right?
Start with a top 3 list of ones you'd recommend based on your findings and see how the cards fall. For me, it's really just a big 2, as I heavily recommend either Linux Mint 13 LTS with Cinnamon 2.X backported (simple checkbox in the software properties menu) or, moreso, elementary OS. Some users out there speak very heavily of Zorin, which aims to be a more Windows centric approach, so you could consider that as well.
I have found transitioning users to elementary OS to be far easier than I expected. I mean, you have a dock with your open or favorite applications. You have your "applications" menu. You open Chrome or Firefox - bam, they know what to do. You open up the applications menu and it's a simple grid of icons listed A-Z. Poke around, find what you need, done. Updates are done via the update manager and everything else a basic user would need is already there. Need some more tools, utilities, or software? Fire up the software center. Of course, a lot of this still applies to Mint, or really any other distro out there, but there's something to be said about starting on a more minimalistic base and building up from there that really makes a lot of sense in some ways. Compare this to a KDE centric environment which has a thousand options in a thousand places and you can see how users of all types (even as a power user I still get annoyed) would frustrate users.
Most importantly of all... listen. If you're trying to push Ubuntu and they don't like Unity, listen to that. Back off that suggestion and see what they think of Mint. If they don't like Cinnamon, try something else. All too often people push *their* favorite distro or desktop environment on other users without really letting the user have a chance to voice their concerns or issues.
For what it's worth, elementary OS is one of the nicer looking distros out there, and it helps that it's extremely, extremely lightweight. If this is a much older system you're working with, it'd be a good candidate (pending that the user in question clicks with it of course).
Good luck!
