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#11
When the retail 7 was first out I ran both 32bit on a second drive while the 64bit remained on the host drive using the same product key. Explaination? Same key = same machine
The recovery partition as well as any recovery disks provided should provide the option for either even with them being branded since you will still be using the same key on the same machine there. The other option for you to decide on is the 4gb maximum according to the specifications which would lessen the need for the 32bit 7 on the other hand.
If you replace the present 2gb with a different brand rather then adding onto the present 2gb with another of the same you would then need a clean install or call MS for reactivation however. 4gb is generally quite adequate since the recommended for the 64bit is about 2.5gb.