Here are some more links for the users of WSS 3.0 and MOSS 2007:
TechNet Virtual labs: http://www.microsoft.com/technet/traincert/virtuallab/sharepoint.mspx
Different Application Templates for WSS 3.0: http://www.microsoft.com/technet/windowsserver/sharepoint/wssapps/templates/default.mspx
You can use these templates as a starting point for building up your own custom applications. Instead of using the generic tables for data storage that some of these templates use, you should define your own schema if you intend to have a concurrent load and high volume.
