I've written a small Windows program that will allow you to easily choose different versions of firmware for your Squeezebox 2 or 3. It's not pretty but it seems to work just fine. I was prompted to do this after walking several folks through changing their firmware. This does not require any restarts of Slimserver, just hit the brightness button on the remote to reload the firmware.
It works by reading in your existing squeezebox2.version file to determine what version you are running and then checks the firmware directory to see which versions you have available. It then simply rewrites the .version file to the version you choose.
It should work on Windows 2000, XP and server 2000/2003 machines but I've only tested it on WinXP. Note this was written using Microsof .NET and thus requires the Microsoft .NET 1.1 framework package to be installed. I suspect that most XP machines will have this already, so it shouldn't be a big deal. If you don't have the .NET framwork, you can download it from Microsoft
here. Be sure to use Windows update after installation as Microsoft has released some updates for the framework.
Since this is a freebie, support will be limited to this thread.

If you want to try it out, you can download it
here.
Any feedback is appreciated. I have tested this running on the machine running Slimserver and also from my desktop across the network to the Slimserver machine. The program stores the path to the Slimserver firmware directory in the registry, so it will remember the last place you selected. At install it uses the default "c:\program files\Slimdevices\server\firmware" as the path it checks. If you did not install Slimserver to that path you can choose another.
Note that to be able to select different versions of firmeware, you need to have more than one version in your firmware directory. You can grab a copy of V15
here and a copy of V28
here. Just save them to your firmware directory if needed.
Other versions available
here.
Again, feedback, good or bad, is appreciated. This is a very simple utility and is not meant to win any awards.

Hope someone finds this useful.
Edit - I found a small bug that would occasionally write the squeezebox2.version file incorrectly and cause the firmware not to switch. This has been fixed and a new version uploaded to the server. The link above now points to the updated version. If you have the first version, please download and install the updated code. Sorry for any inconvenience.
Mike