Locking processes against being killed when low on memory

[Stephen Borrill <netbsd%precedence.co.uk@localhost>]

I'm using NetBSD 4.0 with Xorg, etc. running from flash, i.e. no swap. As 
it's embedded, everything is running as root. Is there any way to tag 
processes as unkillable when running out of memory? Some processes (e.g. 
the X server, management daemon and session manager) need to remain 
running throughout. I don't mind if other things such as web-browsers get 
killed. Currently bad things happen when it starts to run out of RAM...

--
Stephen