The instructions are relevant to Outlook 2003 but of course anything related to the Ribbon or custom task panes wouldn't be applicable.
Unfortunately the VSTO 2005 SE download projects and templates contain a lot of version specific stuff generated by VSTO and won't let you load the project in a VSTO Outlook 2003 addin.
You are able to load the C# and VB
.NET shared addin code or the VB6 addin code and then change the references to Outlook and Office 2003 and remove any Outlook 2007 or Office 2007 specific code or convert it to Outlook 2003 workarounds like Redemption code.
I haven't done it yet but I'm planning on putting up an equivalent set of templates and projects for Outlook 2003 on my Web site soon. I just haven't had time to finish double-checking the code so far.
Those will be projects and templates for Outlook 2003 in VB6, VB
.NET & C# shared addins and VSTO C# and VB
.NET addins, the equivalents of the Outlook 2007 versions.