Started this process 2 years ago. Switched to open source software on windows, then switch the OS to Linux then to OS X, with all the same apps, more or less.

A few good directories for windows FLOSS:

http://www.jairlie.com/oss/suggestedapplications.html
http://osswin.sourceforge.net/
http://theopencd.sunsite.dk/

A few favorites:

+ Firebird/Thunderbird for web/email (get extensions!)
+ Or Mozilla suite for web/email/irc/news/html editing/
+ OpenOffice, can do anything MSO does. Check out Draw, for quick diagramming or flowchart, an added bonus in OOo
+ jEdit as a general text (even xml) editor
+ The Gimp (2.0) for image manipulation
+ Audacity for quick audio edit
+ PuTTY for SSH / WinSCP for secure copy
+ WinPT for gpg under windows
+ rDesktop a remote desktop client for linux (connect to windows servers or winxp)
+ Owl is an intersting new RSS reader
+ Squirrel SQL client if you need to browse DBs

Another tip, nothing to do with the OS but more with migration, make sure your mail server is IMAP. Makes transitions between email clients and platforms really painless.

This list of open source software looks quite comprehensive:
http://damicon.com/resources/opensoftware.html

I have to admit, although I use jEdit for coding, Gaim for AIM, Thunderbird for email, and Firefox for web browsing, I just can't switch from Microsoft Office and Adobe Photoshop to their open-source impostors... OpenOffice is fine, and compatibility with Office is getting better, but it's just not as polished. And The Gimp... is awful. It's only recommended by nerds who haven't used Photoshop. Case in point - the artwork on so many open source projects.

Dan;

I made the full switch from Windows to Linux just over a year ago, and I am still amazed how much of a difference it has made in my day-to-day experience of the computer. I no longer worry about weird crashes, viruses, and all the other goop that seems to accompany Microsoft products. If, like me, you spend many hours a day in front of the machine, switching will make a vast improvement in your daily life.

When you get around to changing your operating system, I highly recommend Xandros. Works like a charm.

Of course, there is some learning curve in switching everything over. But after a month or two on the new system, you will never go back (promise).

By the way, you can fully run the Windows versions of Photoshop (and Dreamweaver, and basically whatever else you want) under Linux using CrossOver and NeTraverse. I don't use them -- the new version of the Gimp is actually quite good -- but it's an option.

Hi Dan,
You'll want to have a look at GIMP 2.0. Not quite photoshop, but not tto far off.
If you were ever a fan of Coreldraw, Openoffice draw has quite a few hidden features(node edit, besier curves).
Lets talk soon!
Good Luck,
Iain