Forcing GRUB to boot prefferred funtioning OS?

[Richard Owlett]

I'm currently physically constrained to using GRUB 1.98, but 
I suspect that my problem will still exist when I move to a 
more current release of my preferred OS.

I wish *ALWAYS* default to the OLDEST installed system as 
that is obviously known to work. [Think about it. If it did 
not work it would be immediately removed.]

I have two machines:
#1 delivered with WinXP Pro SP3 now dual boot with Debian 6.0.5
#2 is my experimental machine. The older (I.E. known good) 
Linux install is a "bells and whistles" install of Debian 
6.0.5. The "newer" (I.E. volatile) install is Ubuntu 10.10.

I'm only interested in installing Debian or Ubuntu. In all 
cases, when offered the option, have chosen to install GRUB 
to the MBR. Both Debian and Ubuntu install media configure 
latest install to be preferred boot OS. That's the opposite 
of my desire.

On machine #2 I expect to install various configurations of 
Debian. I wish to boot only oldest by default.
Machine #1 will only get a new Debian install when Wheezy is 
released. But I will still want WinXP to be default OS.

How can I have it "My way"?  (apologies to a certain 
hamburger chain ;)