There are NO USB 1.1 drivers available for Vista. I have tried to get together with Cypress (manufacturers of the relevant chipset) to get a resolution to this, but I've just not had time to nail it down, and they keep closing the incident within a day.
Do you want me to try? They've been pretty responsive to me (though my first contact with them was to report an error in the ATA2LP datasheet

).
The last release of those drivers was the 6.01 release in 2003 (
link - don't believe the 2008 dates in the article).
I could ask them about releasing the source code (a lot less work for them than making them work with Vista themselves). I don't know if we could redistribute the source or if it would be under an NDA. I also don't know if they have complete sources - they inherited the ISD-200 from In-System Design.