Visio 2003 Software Development Kit (SDK)
Visio 2003 SDK is available as a free download from: http://www.microsoft.com/downloads/details.aspx?FamilyId=557120BD-B0BB-46E7-936A-B8539898D44D&displaylang=en
Check it out.
.NET Tutorial Site
Check out this new .NET/C# Tutorial Site:
http://www.dotnetspider.com/Technology/
It has a lot of step-by-step tutorials for people from beginners to advanced level