Another way to use two (or more) mice at the same time is to use a program such as MultiMouse by Takashi Manabe. It's a daemon multiplexing several mice and making them available through the special device /dev/mumse as a MouseSystems compatible mouse.
According to the author: "This program allows you to use multiple mice at the same time. This program is developed for a subnote user who want to use both a pre-mounted pointing device and a external serial mouse."
I'm not sure if the program supports second mouse other than serial, but the advantage is that the second mouse works in console mode too. MultiMouse can be found at Sunsite (sunsite.unc.edu /pub/Linux/system/Misc) and Tucows (www.tucows.com Linux Console -> Utilities).