Here's a very simple post that will outline the major differences between WSS and SPS Search:
WSS Search:
1. It can index local content
2. New relevance features are used in the result set
3. Alerts & RSS subscription to result set
4.Did You Mean & Dup Collapsing in result set
5. API's provided for Query interface
Portal Search: All of the above plus.....
1. Search Scopes
2. Managed properties based on crawled properties
3. Best Bets
4. Results removal
5. Query reports
6. Tabs in the Search Center
7. People Search/KN
8. BDC Search
9. API's provided for customization for Query and Administration interfaces
Bill English
Mindsharp