That's interesting. Maybe people were complaining about how big the file was (400 megs! Ouch!!!). Yep, that IDT driver was shocking! My sound completely disappeared - the driver rollback worked until I turned off my system, then I had to reinstall the Sigmatel driver.
I believe for computers updated with all updates prior to SP1, the WU version (whether auto or manual) should be 65 MB. However, the standalone download (not from WU) is around 400 MB. In any case, if you reinstalled the Sigmatel driver I would expect SP1 would NOT appear on WU. Are you saying that you saw SP1 on WU after you reinstalled Sigmatel?