1. The VAST majority of drivers will come with whatever Linux Distribution you choose. If the drivers you need don't come with your kernel, then you will either be out of luck (no drivers available), or you will have to download and compile your own kernel with a driver patch. In reality though this is very rare, it's difficult to find a popular piece of hardware that doesn't have at least a subset of its functionality available in Linux.
It's far more common that there is a driver loaded, but it isn't working or isn't configured correctly. In these cases some research on Google and/or a post in this forum should help resolve it.
2. Most probably, I have had great luck with Ubuntu and printer support. I've been able to connect several different printer brands to my machines (HP, Samsung, Dell) and the Ubuntu add printer wizard detected the printer and automagically installed the driver for me. I've used my Ubuntu install to troubleshoot when I was having print issues in Windows.
3. Maybe, it depends on how bloated your XP install had become. Most user-friendly linux distributions (Ubuntu, Fedora, SUSE, etc.) are loaded with programs and services by default. While I'm not sure they are faster than a clean XP install, they don't slow down over time like Windows does.
For what you want to do, Linux should do just fine. The only caveat I have is that the OpenOffice.org suite that most people use for Office in Linux isn't (imho) as good as MS Office. I feel like the spreadsheet and powerpoint applications lack some features, and while compatibility with MS Office documents is pretty darn good, it isn't 100% (usually there are formatting issues, especially with graphics). You can see if this Office suite is suitable for you by trying it out in windows (
www.openoffice.org). Your MP3 player should be fine as long as it isn't a Zune.
I'm a big fan of Ubuntu myself. While it is easy to set up and get going, so are most other desktop-oriented distributions. The main advantage for me is the large user base. If you run into a problem (and you probably will at some point), there is almost always somebody who has had the same problem and posted a fix online. I suggest the 8.04 "Long Term Service" version because it seems more solid than 8.10 and the older codebase will probably be more forgiving on older hardware.