I just bought a replacement case fan (link to Tiger Direct here) and the fan seems to be working great, but unfortunately I was under the impression this fan had speed control. I have checked my BIOS and I can see "SYS FAN 1 SPEED" although it is read-only. Is it possible for me (using Vista) to control the speed of a case fan connected to the motherboard?
Look at Wiki - Fan Control
4-pin connector enables fan speed control. 3-pin connector just enable fan speed sensing. The one you've got is unfortunatelly with a 3-Pin connector.
You need something like this ZALMAN FAN MATE 2 Fan Controller to control the speed.
I have used speedfan and am pretty happy with it, especially its logging features.
If you dont want to run speedfan, this article claims that you can control the speed of any fan inside your box with a simple and free hack: