I use Windows 2000 Professional on my desktop. I do not like Windows XP. I often think about trying Linux on my desktop, but I doubt that I ever will.
For project development purposes I use Eclipse. It is a heavyweight application, but very powerful.
I use Mozilla Firefox for browsing the Internet, and Mozilla Thunderbird for handling my emails. Both are extremely customisable, powerful, and lightweight. They also have excellent standards support, and are secure.