Omega drivers are tweaked ATi drivers. I used this version (which is based on an old version of Catalyst, 5.2) for the
ATi FireGL X1 and
ATi Radeon Mobility M9-P.
In case you want to fiddle around with different drivers, or perhaps the original ATi driver, you can manually edit the .inf file after unpacking the driver. Every supported card is listed in this .inf file and is identified by a vendor ID (VEN_ID) and device ID (DEV_ID). ATi's vendor ID is 1002. The device ID is 4C66.
The rule you have to add is: "RADEON MOBILITY 9000/9200" = M9_ENU, PCI\VEN_1002&DEV_4C66
I can't guarantee this will work with every driver as the actual M9 driver should be in the driver package.
Download: rad_w2kxp_omega_2642.exe