Xorg ABI version

[Ilia Lilov <lilovil@gmail.com>]

I have to use proprietary video driver for SIS graphic adapter. SIS
provides only one binary version of driver, which must use with
certain version of Xorg.
Xorg.log says this:
(EE) module ABI major version (4) doesn't match the server's version (5)

Squeeze has now xorg 7.4, string above for squeeze, and lenny has now
xorg 7.3, string above is the same but it has (1) instead of (5).
Where can I find which subversion of xorg has (4) ABI version, and
where can I find archive repository to downgrade xorg to it?

Thanks, Ilia.