Success! After *much* screwing around and research I got this going -
Windows XP host with SuSE 11 guest OS.

The trick is to install the following packages in the SuSE guest so
that the Guest Additions will install:

make
gcc
gcc-c++
kernel-source
pam-devel
lsb

This all-in-one command string worked on both a desktop and a laptop
for me:

yast2 --install gcc lsb gcc-c++ make kernel-source pam-devel

Once these packages were added, the Guest Additions installed, and all
was well.