I have a functioning SUSE 7.3 system set up as a mail server (postfix & cyrus). It is currently running on an old p-200 mb with 2 SCSI hard drives. Is it possible to simply switch to a modern mb by simply plugging in the existing scsi system?

Any advice will be appreciated.

if you change your cpu, you'll wanna re-compile (I think)

Should be OK. I did it myself (but the CPU change was not drastic, from Celeron to PII, or the other way around, don't remember).

Usually the kernels that install by default in distros like Mandrake, SuSE and RedHat are compatible with pretty much any CPU at or above the "original" Pentium level, so you should be OK. If you get weird errors, try rebuilding the kernel.

If you want to be totally "professional", I would suggest building a kernel optimized for your new motherboard/CPU combo, and having it as an option in your bootloader, alongside with your original kernel.

With regards to SCSI, well, if you have a SCSI controller on your new motherboard compatible with your SCSI hardware (whatever it is) and the Linux kernel, then you should be OK. If you have a SCSI controller card that goes into a PCI/ISA slot on your motherboard, you'll be fine.