Windows 7 transfer to new computer questions

I purchased a retail copy of Windows 7 Home Premium Edition which included both the 32 bit and 64 bit discs. I am currently using the 32 bit version on my computer. I am considering using the Update Anytime online to upgrade to Windows Pro.
In the future, if I build a new computer, can I use the 64 bit disc for install, or am I limited to the 32 bit, since I have already used it? If I can use the 64 bit version, can I still use the key provided for the upgrade to Windows Pro for my old computer?
I don't want to upgrade my old computer to Windows Pro edition if I can't transfer it to a 64 bit version I would need for a new computer. Would the correct sequence be to install the 64 bit Home Premium edition to the new computer, then use the key provided by Microsoft for the Pro version update given to me on the 32 bit update?

Your existing licence will activate 32 or 64 regardless so no problem there as long as its only on one machine at one time and as its retail copy could be moved to new machine, regards the upgrade I think the upgrade would technically be meant for the same machine although it may work on another I think you would prob be violating the EULA
Hopefully someone else will clarify with a bit more certainty

Full Retail licenses can be moved to new machines with no problem - although telephone activation will almost certainly be required.
Your License is for a single installation - so you cannot install both the 32-bit and 64-bit versions at the same time.

An Upgrade license subsumes the base license into it - so the base license is NOT available for use on any other machine.

If your license is a full retail one, then you can use it on any machine you like - if it's an Upgrade, it must have a qualifying license available for the machine on which it's being installed.