Here some links I've come across that I've found helpful
Building a Hello World Web Part for Windows SharePoint Services 3.0
http://aspalliance.com/1480_Building_a_Hello_World_Web_Part_for_Windows_SharePoint_Services_30.all
Based on this Ted Pattison video: http://go.microsoft.com/?linkid=6471616
Creating and Using Event Handlers in Windows SharePoint Services 3.0
Video: Ted Pattison
http://go.microsoft.com/?linkid=6471621
Creating and Testing Features with Windows SharePoint Services 3.0
Video: Ted Pattison
http://go.microsoft.com/?linkid=6471617
Creating a Custom Page Layout with SharePoint Server 2007
Video: Ted Pattison
http://go.microsoft.com/?linkid=6471618
Creating and Using Site Columns in Windows SharePoint Services 3.0
Video: Ted Pattison
http://go.microsoft.com/?linkid=6471619
Creating and Using Content Types in Windows SharePoint Services 3.0
Video: Ted Pattison
http://go.microsoft.com/?linkid=6471620
Creating and Using Event Handlers in Windows SharePoint Services 3.0
Video: Ted Pattison
http://go.microsoft.com/?linkid=6471621
MSDN Webcast: Developing SharePoint Workflows Using Visual Studio 2005 (Level 200)
http://go.microsoft.com/?linkid=6471622
SharePoint Server 2007 SDK: Software Development Kit
http://www.microsoft.com/downloads/details.aspx?FamilyId=6D94E307-67D9-41AC-B2D6-0074D6286FA9&displaylang=en
Windows SharePoint Services 3.0 Tools: Visual Studio 2005 Extensions
http://www.microsoft.com/downloads/details.aspx?familyid=19F21E5E-B715-4F0C-B959-8C6DCBDC1057&displaylang=e