You might want to use regular expressions to do this:
$id = "TORK34";
ereg("^([a-zA-Z]+)([0-9]+)$",$id,$regs);
The ereg()-function compares the string in $id to a search pattern, in this case "([a-zA-Z]+)([0-9]+)$", which means: "find 1 or more letters from a-z or A-Z and then find 1 or more numbers from 0-9". The parenthesis are there to save the data in an array. The $regs-array looks likethis after calling the function:
$regs[0] = "TORK";
$regs[1] = "34";
which is what you need.
I might have gotten the search-pattern wrong, but try it. You might want to get into regular expressions a bit anyway, since they are a powerful tool.