Merging two linked lists C++

Hello /prog/

I'm having some trouble with a function that is supposed to merge two linked lists. I'm being passed two Linked Lists as parameters and want to know an efficient way of making it so that I can merge these two lists together (duplicates are allowed) without using an insert function. The code that I have is here:
http://pastebin.com/RtUGcYhy

Any help/suggestions/criticism will be appreciated.

You should avoid writing your own code when you can just use the standard library. It has platform-specific optimizations, and is much easier to maintain.