You can find programs out there that will move your applications settings/preferences over to the new hard drive, but you will have to manually install each application using the disks/downloads they came from.
I could be wrong but I'm not aware of any applications that will move your applications over from one pc to another, due to legal reasons.
Your other option, though, would be to use the old hard drive as an external, like you said, and just run those applications off of that drive. The applications will load slower, but it would work.