martyphoto,
welcome to
RP!
the short answer is no, you cant just move them over to the external drive. or at least, not if you're running any windows since win98. all of the registry entries are tied to the location where the program currently resides.
also, you wouldnt like the speed having the program on an external drive. externals are slower by quite a bit.
so, basically, if you just really have to have it on the external, you can uninstall your current version and install it on the external. you might even be able to get copies working on both the external and internal, but if you're space saving then i doubt you'd want that.
now, i gave you the short answer as no. however, there used to be a program that came with 'Partition Magic' that would not only copy your program files to a new location, but it would also change the necessary registry entries from the old to the new. the program was called 'Magic Mover'. i dont know if the current versions of partition magic still come with this extra or not.
typically, externals are used for not often used data files, storage, backups and that sort of thing because of their slower speeds. they typically run through usb or firewire and both are quite a bit slower than a native ide port transfer. buy hey, i'm not telling you you cant do it
Craig