Microsoft used to offer a helpfile named msi.chm with lots of info about Windows Installer and MSI files. Officially they have stopped offering it in this format. They refer to online docu and files in a new format, that Windows XP cannot display. But Microsoft included msi.chm in their freely available WiX, which can be found on wix.sourceforge.net.
Download for example WiX35.msi, use 7Zip to extract the file WiX.cab, then double-click on that file to open it in Explorer (not in 7zip) and look inside to find the file msi.chm.
keywords: MSI, helpfile, msi.chm, msi.hlp