www.microsoft.com/.../evaluationoverview.asp

I believe the STS was renamed WSS and is the free component of SharePoint. SPS is the aggregation tool that is built upon the WSS technology. SPS 2001 was first, followed by 2003 which is more integrated with MS Office suite.

This is a simplistic explanation, but I hope it helps.

About the only similarity between portal  2001 and portal 2003 is the name and some of the search components.

From a very broad perspective, WSS is the collaboration engine for the SharePoint package and SPS is the aggregation/audience targeting/search & indexing/ taxonomy engine for the other part of the SharePoint package.

You can run WSS without SPS but SPS requires WSS. WSS is free. SPS is not.

Checkout the following two whitepapers we wrote for the sharepoint  product group:

Microsoft SharePoint 2003 Products and Technologies: Technical Overview

Migrating from SharePoint Team Services and SharePoint Portal Server 2001 to Microsoft SharePoint Products and Technologies

The links can be found here: http://www.parallelspace.net/sharepoint/

No, the current MS SharePoint 2003 migration white paper doesn't cover SPOUT and SPIN.

... but we are working to complete a second SPS 2003 "Advanced Migration" white paper that will cover 5 advanced migration scenarios and touch on SPOUT and SPIN.

The best documentation for the Document Library Migration Tools is a ~12 page HTML "help" file that installs with the tools that describes several specific SPOUT/SPIN migration scenarios, reference information, FAQs, known problems, etc.