I have three.
One is Pentium 4 I built myself in 2001 ($$$$$$... boy was I young and stupid back then
). I use it as my "server" computer. It runs MS Windows 2000 Pro, but I am looking to upgrade it to Windows Vista Ultimate in January. Though, I might push that back since RDRAM is still expensive.
I have an HP laptop that I use as my main computer. In fact, all of my computer use is done on my laptop in bed. (Hey, it is COMFY surfing the net in bed!) It runs MS Windows XP Professional.
I have a third computer. It is a desktop that will be a Celeron. It has an AMD K-6 motherboard in it, but it is starting to go. I have a spare Celeron/PIII motherboard and processor that I will put in it. I am actually going put it to use as a "WeatherScan." I will use the Task Scheduler in Windows to have it automatically run Taiganet's WeatherStar 4000 emulator. What I want to do is install the 4000 emulator twice. One copy of the emulator using the city that TWC uses for my local forecast and another copy for a town south of me. Depending on time of day, I can program the Task Scheduler to change my forecast city. I then will use a video card with S-Video output and connect it to an auxilary input so the emulator will show on my TV. So my "AUX" channel will be a mock WeatherScan featuring the 4000 emulator. I will set the emulator to have a long local forecast (like 3-5 minutes). I have a spare Windows XP Pro license for this machine, so that is what it will run. (Now the decision is whether or not I want to make it "broadcast" on every TV in the house.) I will also utilize this computer for extra network storage.
I had a fourth computer, an Emachines Etower, but the motherboard died so I parted it out. It lasted 7 years, so I cannot complain for a supposedly cheap computer.