Internet Explorer Add-In to load a Template into Mailform of MSN, GMAIL, Yahoo

for a "small" Internet Explorer Add-In I need Help at Development. I will automate MSN, GMAIL and YAHOO!Mail with my exist solution that creates Signatures. So in a "Mailform" of MSN Mail (Live-Mail) (for Example) it should load a Template? (from a local Source, Filepath) If required tool from add-in-express for IE and .NET is possible! it should be written in VB.NET. --> For example it should ONLY IE Add-In like is on [login to view URL] (is a free tool)