Update on 2013-04-28: New version!
After I've published this script I found another approach I'd stopped to work on some time ago. Now I've spent some more work on it, and finally got a reasonable result. It seems to solve all text rendering issues, but it prevents the system's default animation for button state changes and some button states on Win Vista and 7.
The very last changes are only tested on Vista, but I hope they will work on other versions also.
Spoiler