I know that it's been a long time since I opened this thread. Well, at some point in time, i managed to solve this problem by using a dual boot (slackware 12.1 and [ubuntu 10.10]/[ubuntu 11.xx]/[slackware 13.0]/[slackware 13.1]/[slackware 13.37]/[slackware 14]) and using grub instead of lilo as boot manager. To be more specific, when I had dual boot with ubuntu, I installed grub from the Ubuntu CD; when I had dual boot with slackware [13/13.1/13.37/14] I installed the newer slackware, with lilo and then installed grub on slackware 12.1 and used that grub. Today I wiped out the slack 14 in order to make room for the "OS Who's Name Shall Not Be Spoken" in it's seventh version (Yes, I had no trouble not having it for some years now, but I have to do some work using Global Mapper and since my laptop has only amd turion at 2ghz and only 2gb of ram there would be too much time consuming to run the application in a wm). After installing that O.W.N.S.N.B.S. I booted into slackware 12.1 and reconfigured grub so it could boot Slack 12.1 or the O.W.N.S.N.B.S. All well until rebooted and saw that the problem with mouse reappeared. Maybe it worths to say that I made no change to the slack system all these years so I don't think this might have something to do with udev (or it might but I can't understand how or why). Oh, and there is another thing: for now there is no more a problem related to my first usb port. It's related to any USB port (although I have only two).
P.S. I am sure that running any Slackware (from 13.0 to current) alone wouldn't get me this issue but I want 12.1 because of kde 3.5.x, wich I'm used to it, and because of beeing too lazy to install and configure lots of 3-rd packages I allready have working on 12.1.
P.S.2: maybe it's related to X config?