Often when I find an article in the SQL Server BOL I see that the article has an address of ms-help://
but I can't forward this "uri" to a colleague who doesn't have the Sql Server BOL --- so the question is is there a consistent mapping between ms-help:// and http://msdn.microsoft.com
Honestly, my answer would be to use the msdn for everything, unless you're personally offline and don't have access to it.
If you like using the MSHELP application, it is possible in the settings to make it use msdn online, rather than local content (this is the default if you don't bother installing the local docs anyway).
This means you always have the msdn link (even in the help application) and therefore can share it with your colleagues.
MSDN online changes at a different pace than your offline content. Ie. the mapping function may be valid today but invalid tomorrow. What I do I just search the topic title in msdn (using google site:msdn.microsoft.com of course, msdn search is just lame) and the post/mail the link.