i think there is no string split funktion in rockbox.
so you have to do it by hand, either by searching for your seperator with pos = strchr(string,":")
and copying the parts,
or by stepping through the charakters of the string, copying each char in another buffer, until you reach your seperator.
If you arent familiar with string handling in c, google for a tutorial, theres much doku about string handling in C.