Depending on the default kernel you loaded will guide as to what modules might be needed to provide usb support. To list what modules are actually loaded use the "lsmod" command.
For a non-usb enabled kernel like bare.i,
modprobe usb-uhci (or modprobe usb-ohci)
mount -t usbdevfs none /proc/bus/usb
The modprobe command above should autoload the module usbcore. Also, there is a uhci module. Not sure what the difference is with usb-uhci though.
For a usb enabled kernel like usb.i, then just
mount -t usbdevfs none /proc/bus/usb
Either should mount your usb file system so that
cat /proc/bus/usb/devices
will produce output. Allbeit difficult to read. But the lines that start with "T:" I believe identify a new item. Also, I have found the output from the command "dmesg" of great help as well. If you plug and unplug the device a message is usually added to the end of the output.
SuSE could have other addin modules as well that are not part of the standard kernel support. Also, SuSE 8.1 is based on the 2.4.19 kernel and it has considerable more support for USB and Firewire devices than the 2.4.18 kernel does in Slackware 8.1. Also, do you know what module SuSE was actually loading for the Speedtouch?
For your mouse, a usb enabled kernel should support it, and on a non-usb enabled kernel after uhci (or ohci) support is loaded;
modprobe hid (or modprobe usbmouse)
modprobe mousedev
That should also autoload the module "input" as well. The mouse is normally on /dev/input/mouse0. If want to set the default device, /dev/mouse, to it then;
ln -sf /dev/input/mouse0 /dev/mouse
You didn't state the type of modem the Speedtouch is. But when I searched the only references I could find are for a ADSL modem. Now if your unit is an ADSL modem then you might want review the following link for some driver information.
http://www.qbik.ch/usb/devices/showdev.php?id=629
and there is an ongoing project here;
http://sourceforge.net/projects/speedtouch
Perhaps it will be of some help.