For 2.4, the modules end with .o; for 2.6 they end with
.ko
Dynamically loaded at run time
Kernel modules are controled by modutils package, which includes commands:
lsmod #lists loaded modules
rmmod #unloads a module
insmod #loads a module
modprobe #loads a module with its dependances
modinfo #gives info on a module
Module dependences are stored in
/lib/modules/<version>/modules.dep
and generated automatically by depmod command at system startup.
Module parameters (IRQ and addresses) and aliases: /etc/modules.conf
To update it, modify files in /etc/modutils then run