The driver isn't in 2.4.20, but rather can be found as a patch from the scsi-maintainer's website (i.e. http://people.freebsd.org/~gibbs/linux/ ). The patch is does not change any files in 2.4.20, merely adds the aic79xx driver. Our system's mainboard is a SuperMicro X5DA8 I'd suggest adding it to your kernel, as there is no alternative for the hardware.
this is in all the latest livecds
oops, fixed