You can use the LIST function in a calculated field pointed at your Quicktime field.
But, in addition to listing the file path, it will also list the size, etc.
The List() function is not required. Use GetAsText ( YourContainer ) to get the size, relative and absolute path. Use GetValue() to get the last value and substitute out the "moviemac:" or "moviewin:" prefix.
GetAsText and List both return the same results.
Thanks for the heads up... They may return the same result in this case, but IMHO it's best to use each function for its designed purpose.