This probably belongs in the Networking forum, but have you checked out Ciscos website? They usually have some pretty good info.
Otherwise from my experience with 2500s 2600s and 3500s (not Catalysts, I think Catalysts have a different type of IOS). first you need to go to enable mode, then config mode, then specify the Interface, then duplex half and speed 10
these should be your commands
enable
config t
interface ethernet 24 (or fast 24) (or I think in the newer ones fast 0/24)
speed 10
duplex half
You can also use the "?" command at any time to figure out what valid options you have.
Edit: Also don't forget to save the config by using
write
or on some of the older ones
copy run start