Support for that card is standard in recent kernels. E.g. 2.4.17-rc1 has
Highpoint 370 software RAID
I doubt you'll actually need custom install disks. AFAIK, it should be
possible to install Debian on the first disk using the regular boot
floppies, then build a custom kernel to support the card and then set up
mirroring.
Well, i have to get that version of the kernel with the RAID support turned on onto the boot disk somehow. You see, i can't install debian if it can't see the hard drive i have to install it on :)
So how do i get a new version of the kernel onto the boot disks?