Just about any response here on the list would be incomplete and a
mixture of duplicated information. I'd recommend one or more of the
following links:

This lists team  Services and portal  Server side by side, including core
function, search, customization, document management, etc. It's also
the "official word".
www.microsoft.com/.../technolog
ies.asp

To get close to the same thing for SPS v2 (and WSS, which is the
replacement of STS), read
www.microsoft.com/.../relationship.asp

Differences between sts  1.0 and WSS
http://wss.collutions.com/default.aspx

Also, do a quick google.com search for

sharepoint "team services" vs "portal server" comparison

and you'll get some more hits.