prep 4 sarge 2 etch upgrade; patching driver

[Mark Copper <mcopper@titaninterface.com>]

I posted 2 days ago on this old, old topic, but am posting separately
now to ask a more general question about patching sources.

I'm planning to upgrade sarge to etch remotely.  The tricky point for me
is to include a driver for the RAID card on the box (Adaptec
ASR-2420SA).  Etch does not support this card as reported in 2/2007 on
this list.  Indeed, checking aacraid.h in 
linux-2.6.18/drivers/scsi/aacraid shows the AAC_DRIVER_BUILD to be 2409
where the later 2420 is needed (and available from adaptec.com).

Previously I simply overwrote the old /drivers/scsi/aacraid source files
with the new ones and recompiled the kernel.

Is there a better way to do this?  Should I check later versions of the
kernel to see when/if the updated driver entered the kernel source?  And
if I do that, is there a Debian way to use a newer kernel while keeping
everything else rock-solid stable?

Any pointers, even if just to appropriate docs, is greatly appreciated.

mark