I have seen this kind of problem reported here before, but I still can't get it to work despite having tried all the options presented in those threads. The kernel was compiled with CONFIGURE_USB_HID=y and I tried every protocol in xorg.conf but it still won't work.

The mouse is properly powered up and the PS/2 protocols allow some very incorrect movement, but that's it. Also, Fedora Core 4 identified and used the mouse without any problems.

Anyone knows how to solve this problem in this computer/distro?

Have you tried mouseconfig?

Btw. Dell Inspiron is a laptop i guess? If so you probably want to have both your mouse and touchpad working at the same time. If you do you have to edit /etc/X11/xorg.ocnf and add an extra pointing device.

Yes, the Inspiron 5150 is a laptop. I didn't know of mouseconfig, thanks.

I changed the usb mouse for another model and it worked properly this time. I don't know the reason, as it worked under both Windows and Fedora. Maybe there's a problem with the USB drivers?

The touchpad also works when using the ps/2 protocol, but the usb mouse doesn't work if this is enabled. However, I haven't tried solving this yet and it seems there's info on the net about it.

Well, if you were trying to use PS/2 protocols for a USB mouse, that's your problem right there. PS/2 protocols are for the PS/2 port (the one with the bunch of pins, like on a normal mouse). You'd need to change the settings to USB instead of PS/2. Even so, I've seen some very finicky USB mice in Slackware. The EASIEST way around your problem for that particular mouse is probably just buying a USB-to-PS/2 adapter (they are very, very cheap).

I have an IBM T23 using both internal "knob" and external USB mouse simultaneously. Try editing your xorg.conf silmilar like this example.

Section "ServerLayout"
Identifier "XFree86 Configured"
Screen 0 "Screen0" 0 0
InputDevice "Mouse0" "CorePointer"
InputDevice "Mouse1" "SendCoreEvents"
InputDevice "Keyboard0" "CoreKeyboard"
EndSection
...

# This is the TrackPoint
Section "InputDevice"
Identifier "Mouse0"
Driver "mouse"
Option "Device" "/dev/psaux"
Option "Protocol" "PS/2"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection

# This is the USB mouse
Section "InputDevice"
Identifier "Mouse1"
Driver "mouse"
Option "Device" "/dev/input/mice"
Option "Protocol" "IMPS/2"
Option "Emulate3Buttons" "no"
Option "ZAxisMapping" "4 5"
EndSection

Everything is taken from http://www.math.uakron.edu/~chad/linux_t23.html found from http://www.linux-laptops.org/.

The point is that you add an extra pointing device which isnt CorePointer so it doesn't have to be present when you want to startx. The USB interface also enables hotplugging/unplugging without breaking X.

If I've had my laptop here at work I could have posted the entire xorg.conf. I can post it later today if you want it.