Sounds like you boot to graphical logon. And X doesn't work well with strange new mice.
You may be able to to a text terminal and log in. Then you can fix your XF86Config file to work with new mouse.
You can also pass paramaters to lilo when booting, ie: 'linux 1' or 'linux 3' to boot to runlevel 1 or 3 and avoid graphical login (Assuming your kernel-image name is 'linux'.) SuSE may even have a 'fail-safe' configuration installed that you can select from lilo menu/prompt. I forget,
bash-2.05$ uptime
3:53pm up 95 days, 6:55, 6 users, load average: 1.16, 1.15, 1.16.
I Don't reboot much.
Good luck and have a lot of fun...
Dan Dofton
Hangin' LuSE with SuSE