Microsoft SharePoint Services version 2 - Web Links on customizing / adding functionality using site templates, web parts and Office document viewers.

http://www.microsoft.com/technet/prodtechnol/sppt/wssapps/default.mspx

http://office.microsoft.com/en-us/assistance/HA010449811033.aspx

http://office.microsoft.com/en-us/assistance/HA011228651033.aspx

http://www.sharepointcustomization.com/default.aspx

http://www.microsoft.com/sharepoint/downloads/components/default.asp

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/odc_sp2003_ta/html/ODC_SPSCustomizingSharePointSites1.asp

http://www.microsoft.com/windowsserver2003/technologies/sharepoint/default.mspx

http://office.microsoft.com/en-us/FX011204871033.aspx

http://office.microsoft.com/en-us/FX011683571033.aspx

http://office.microsoft.com/en-us/assistance/HA011709791033.aspx

http://office.microsoft.com/en-au/assistance/ha011402701033.aspx