Both my Omega and my IYONIX have the very same ALi M1535+ southbridge inside. ALi says that the M1535+ only supports ATA100.
There are, however, M1535D+ southbridges where the very latest revision apparently supports ATA133. However, neither my Omega nor my IYONIX have one.
Anyway, it is a non-issue. ATA100 and ATA133 are very similar in their performance characteristics, the differences are usually not detectable. And many modern drives only support ATA100 anyway - Hitachi/IBM, Seagate and WD. ATA133 seems to be a Maxtor thing. I guess we will see Serial ATA taking over instead of ATA133 getting a standard thing.