I don't think your old Vista hard drive will boot up into Vista, it will have the wrong motherboard drivers on it. Also Vista will have been activated on the hardware hash (identity) of the old pc. Some say that a Repair Install sometimes works. You could try that out by removing the new harddrive W7 and connecting the old drive in it's place and then boot up.
To get the Boot Manager to dual boot requires one of the OS's to be clean installed AFAIK click here