So you've read through this howto a dozen times, done everything exactly as you think you should have, and your mouse still doesn't work? The best advice I can give you is this: experiment. Sure, it's a pain in the posterior, but in the end the only way to find out what is going to work with your mouse is to try all of the alternatives until you have success.
As always, if there is something you don't understand, try reading the manual page first and see if that helps. If you have a specific question, or a problem you think I might be able to help with, feel free to contact me at the address listed at the top of this howto, and I'll see if I can help you out or point you to someone who can.
The comp.os.linux.setup newsgroup or comp.os.linux.hardware is the appropriate forum for discussion and/or questions regarding setup --- please don't post questions to other groups, and especially don't crosspost questions to two or more of the Linux groups, they are more than cluttered enough as it is! When posting, you will get a much better response (and much fewer flames) if you use appropriate Subject: and Keywords: lines. For example:
Subject: BUSMICE - Gateway 2000 mouse wont work. Keywords: mouse busmouse gateway
The following are useful resources for information regarding Linux and Mice.
The 3-Button Mouse HOWTO is of great use if you have a combination 3-Button Serial/PS2 mouse. It gives pointers on how to get the middle button working.
The Linux Laptop-HOWTO gives pointers on getting external mice working along with your built in mouse.
Wacom Tablet HOWTO gives pointers on using the Wacom Tabel as a mouse.