require EXPR only accepts Class/Name.pm style module names, not Class::Name. 
How frustrating! For that, we provide load_class 'Class::Name'.
It's often useful to test whether a module can be loaded, instead of throwing 
an error when it's not available. For that, we provide try_load_class 
'Class::Name'.
Finally, sometimes we need to know whether a particular class has been loaded. 
Asking %INC is an option, but that will miss inner packages and any class for 
which the filename does not correspond to the package name. For that, 
we provide is_class_loaded 'Class::Name'.

WWW:	http://search.cpan.org/~sartak/Class-Load/