Best method of transferring your old rig to a new one?

[Dhaladog]

I currently have 2 external hard drives attached to my old setup both are pretty full, could I transfer both of these incl the C Drive to a new PC and is it true that you cannot transfer any programs, games incl passwords or log ons, if so I really don't think I want to do it as it would be such a pain having to re-download everything again and then attempting to log in to all the websites.