As I understand it, editing the _vimrc file is the way to add keymap commands yet it ignores such commands. Eg:

noremap :!C:\Development\Flash\FLEX\bin\mxmlc.exe %

autocmd BufRead *.as set filetype=actionscript

These are not being read (with or without a preceding colon) though they work from the command line (within vim)

Where do they need to go?

The default location on Windows is ‘C:\Program Files\Vim\vim72′ (with an additional ‘Vim’ directory); then Vim looks for the global config in its parent directory, i.e. ‘c:\Program Files\Vim’. You can also add system-wide plugins, dictionaries and other stuff into ‘c:\Program Files\Vim\vimfiles’ without polluting your actual installation, so you can update it without having to remember which files you added or changed.

This works in Windows 7 (64 bit with 64 bit Vim) as well as in Windows XP (no Vista here, so I can’t tell).

Also it wasn’t necessary to set the HOME environment variable. Vim’s default is to use %USERPROFILE% (or %HOMEPATH%, I’m not sure if there are cases where they can differ; in your case ‘c:\users\dave’) and to map it to $HOME.

By the way: Starting the config files with an underscore instead of a dot is optional and only used for user-convenience. ‘.vimrc’ is a perfectly acceptable file name. At least in Windows 7 you can even create (or rename) a file with a name starting with a dot. But even if this doesn’t work in XP or Vista, you can still create such files from the command line or from within Vim (which you will most likely use anyway if you’re creating ‘.vimrc’).