We are a family of gentle typists, so our keyboards have a tendency to last a long time. I purchased my last keyboard in the mid nineties, before the era of extra multimedia or internet specific keys. Now that an even older no-name keyboard (from the first batch that incorporated the Windows Key) is getting slightly quarrelsome, I took the opportunity to purchase a Microsoft Comfort Curve 2000 for a very reasonable AU$15.
After plugging it into my Windows 2000 box my first task was to try every single multimedia button. I didn't install the recommended Intellitype driver, as I wanted to see how it would go without it, and was keen to keep the PC free from unnecessary software.
Most buttons worked straight away. The calculator and web/home buttons had no effect, and the mail button brought up the computer's unused default email program of Outlook Express. This household are Gmailers, so my first task was to fix that.
The options for default email application in Control Panel | Internet Options | Programs were Outlook Express and Windows Live Mail. To add the Gmail option Google recommend installing their Gmail Notifier application, but if you're not scared of the registry then you can just make a few simple changes yourself, as described in the Google book preview of Fixing Windows XP Annoyances. I took that path, and got the mail key hooked up to Gmail within minutes. (Update 8-Aug-2010: the Annoyances page links to a now non-existent file, but you can find similar information on the Ask Mark site.)
I had a brief look at the two ineffectual buttons, but was unable to get them going. According to RegMon the Web/Home button was calling up Firefox, but I think it was being passed some empty parameters that caused it to abort. Interestingly, when I set Internet Explorer as my default browser that button worked perfectly. The calc button, according to RegMon, did absolutely nothing.
In Windows ME, XP and later these extra buttons have a nice new registry section devoted to them. Each button has a particular constant, and this can be used to direct windows what action to take when that button is pressed, as described by Microsoft. For example, Mail is assigned the subkey number of 15. You could then set key 15 to run the program "Notepad.exe", or more realistically, just tell it that key 15 should run the system's default mail program.
Although the Microsoft article indicates this applies to Windows 2000, my 2000 SP4 does not have those AppKeys, and when the bonus buttons are pressed those AppKeys are not referred to. Instead, it just seems to use some sensible defaults, but it does make it hard to work around those defaults.
You can read about the fun other people have had with multimedia keys on the DVBOwners Forum and the Riff Blog.