hardware switch to select from menu

[Frans v.d. Klip]

Hi,
I am setting up a home server with a D510MO board (Atom 510, 1 GB ram, 
2x 1.5TB hd sata, 4 GB internal USB flash disk for OS, on-board Intel 
video) using Ubuntu Server 10.04 in a small case. The system will have 
no keyboard, no display.
Once operational, most system settings will be made using a web-bases 
management tool (probably eBox).

For troubleshooting or maintenance (disk backup) I would like to boot a 
second OS (like System RescueCD, PartedMagic, Xubuntu) from a reserved 
partition on one of the hard disks, but without keyboard/display there 
is no way to either make a selection from the grub boot menu or the bios 
boot disk selection.

Is there a way in grub (v1.98) to choose from the menu using a hardware 
switch (or data file)?

I can wire up something to the RS232 or parallel port.
The normal boot disk (with Ubuntu Server) will be on the dedicated, 
internal USB flash disk connector and I doubt the USB boot order in the 
bios can be set to boot (a grub bootable stick) from one of the other 
USB ports (the flash disk has not yet arrived).

Thanks.
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Met vriendelijke groeten / kind regards,

Frans van der Klip