Okay, I've been using Linux for about a year, so I'll help where I can.
The network thing is out of my league - I have virtually no experience with networks nor any high-speed internet (only slow dialup for me). I'll let some else handle this one.
If you have those MP3's, documents, etc. backed up, then you'll have no problem copying them to Linux and accessing them. There's a Winamp clone called XMMS (not to mention a zillion other media players out there). Office files like word documents, etc. can be used with OpenOffice or StarOffice - both good replacements for MS Office. Pictures and other things can be handled with the window manager of your choice.
It's true, Linux at it's most basic is command-line based - even early versions of Windows were built over DOS before NT came along. The same can be true with Linux - XFree86 is a large program that allows you to run a GUI (graphic user interface) over Linux. Two of the most popular window managers for XFree86 are KDE and Gnome - both are very easy for Windows users and are packed with features (not to mention they're much more customizable).
Linux is slightly slower when it comes to hardware. Basic things like most motherboards, monitors, cd-roms/rw's/dvd-roms/floppy/hard drives work fine - their "drivers" are built into the kernel and most of the time Linux can handle these devices and especially ram better than Windows can. Other things like sound cards, modems (winmodems are bad), and video cards need some further research before you know if it's compatible or not.
Everything above that I've mentioned is pretty much free - including a billion programs (freshmeat.net). This is because no one really owns Linux and the source code is available to anyone - same goes for most programs. So if you want to, you can download most distrobutions for free and then create a cd to install it from. If you don't have the bandwidth for it - you can have someone download and burn it for you, only asking for mostly shipping costs.
http://www.tuxcds.com/ is a good place for that - you'll find the latest Red Hat under XXX XXX 9.0 (they hide the name because Red Hat asks them to). Otherwise, I would buy the distrobution from a store or from the distros site. Why? Because you'll be supporting the people who develop it.
My advice to you is to find a book. There's boards like this one and linuxquestions.org where people are glad to help you, but having a book on hand is a good resource - otherwise you'll be posting a lot of threads before you're through. Give Red Hat or Mandrake a shot though, the gui installer is a breeze, they include a lot of programs like the ones I mentioned, and they make the switch a lot smoother (rpms to install progs, little or no command-lines) and they set up a window manager like KDE or Gnome for you, assuming your video card is compatible. Have fun and good luck!
[ August 01, 2003: Message edited by: Meshuggener ]
[ August 03, 2003: Message edited by: Meshuggener ]