Hmm, ok, your graphics card is good. is it sharing an IRQ with anything else, particularily your sound card or network card?
Your mouse and keyboard. Are they both USB? If so, is the mouse wireless and or an optical mouse? (the ones with the laser in the bottom instead of a mouse ball) If that is the case, try plugging the keyboard into the PS2 keyboard port using the supplied adaptor, and continually move the mouse during sign in to see if that prevents the lockup. Some optical mice, particularily the microsoft Intellimouse Explorer have a "sleep" mode where they go into powersave, and everquest occasionally does not detect them, especailly if the mouse and keyboard are both on USB. You can sometimes fix that with an Alt+Enter into windowed mode and then back to normal screen. You also may want to make sure you have the correct mouse driver installed and not just the system default driver (or make sure you don't have BOTH installed, that will cause the same issue)
What brand mouse are you using?