> Isn't the Ultra 1 a 32bit machine?

if uname -a tells you UltraSPARC, and sun4u, then no.  All Ultra* systems
are 64-bit AFAIK.

> Solaris 7 seems to think mine is.

Yeah, but systems like the Ultra 1 and the Ultra 2 don't boot into the 64-
bit kernel by default, so you have to configure it.  You might want to
edit /platform/platform-name/boot.conf and set

ALLOW_64BIT_KERNEL_ON_UltraSPARC_1_CPU=true

If that doesn't work, you should update your PROM.
Just my $0.02