I know OpenOffice, for example, handles Micro$oft's native format, and the GIMP handles Adobe's .psd format. Not so sure about spreadsheets- my only experience with those and free software was when I was trying to mod a game that used a spreadsheet for some of the units, and the Micro$oft macros programmed into the file didn't function properly.
But that was one and only one incompatibility. I'm uncertain of others.
Basically, if you are curious and want to know if you can safely migrate to linux, consider what types of files you use and check for open source apps that support those formats. You can do this from Window$, actually; most open source software options you'll find during your search have a linux version as well.
Keep in mind, linux comes with a compiler (which Micro$oft and/or resellers historically charge a
firstborn child for), so you may end up having to compile from source. For Window$ uses, this can be scary the first time you do it, as the screen fills with what looks like trash (sometimes for a very LONG time indeed), but you get free software out of it.
And cake. Lots of cake. :silly:
Try
http://www.ubuntu.com/">Ubuntu linux first. I understand it's supposed to be easier to use than other flavors. Good luck!