How can I install swype on HTC Wildfire S?
Swype uses a "closed" beta system to distribute its app rather than using the Market. You can register for the beta and get a download link for their installer by simply visiting the Swype website.

Disclaimer: I have no idea if the Wildfire is "officially" supported, but QVGA screen support is noted for v3.0. The forum thread you linked to in your question is about 5 months old, and QVGA was not supported at that time.