Check the Microsoft ::shudder:: or Apple Style Guides. The plural is referred to as “mouse devices.” Case closed.
Sorry, but I’m a tech writer and I come across this kind of crap every day. Don’t get me started on realtime versus real time. One’s an adjective, and one’s a noun. (You can perform realtime editing … You can export your project in real time.) Even the idiots at Apple and Adobe (whom I’ve spoken to in countless conference calls) don’t get it. They avoid it by hyphenating it at every instance in their documentation. What a cop-out.
BTW, I hate Windoze XP. More on that to follow.