if you look at the error message that Win7 pops up, it will lead you to Here , where you can download a program called WinHlp32.exe for a variety of OS versions (8.x, 7, vista, Server 2k8)
How old is your copy of mIRC? The help files have been in .chm format since v6.21 that I know of, and maybe earlier than that. (and Windows 7 can open .chm files)
I refuse to engage in a battle of wits with an unarmed person.