if i remember correctly it should not matter. they are both on the same disk. when you buy win 7 you are not asking for 32bit or 64bit, so the key should work for either install.
System Manufacturer/Model Number self built OS Win 7 X32 CPU e8400 Motherboard asus rampage formula rev. 1 Memory 3.5 gigs ddr2 Graphics Card geforce 9500 gtx Monitor(s) Displays 26" Screen Resolution 1680 x 1050
You get two DVDs one is 64 other is 32. One key to be used for either. In fact you can go from 32 to 64 back to 32 as many times as you like. But only one computer at a time. Enjoy.
OS Windows 7 Ultimate x64 SP1 CPU Intel Core i3 530 2.93 Ghz Clarkdale Motherboard ASRock P55 PRO/USB3 LGA 1156 Memory 4 GB OCZ DDR3 1600 (PC12800) Low Voltage Desktop Memory Graphics Card Nvidia GeForce GTX 550 Ti with 1 GB of RAM Sound Card Realtek HD ALC892 Monitor(s) Displays 20'' eMachines E202HDbmd Glare Panel Widescreen Screen Resolution 1600 x 900
Keyboard Microsoft Wireless Optical Desktop Elite Mouse Microsoft Wireless Optical Desktop Elite PSU Rosewill Xtreme Series RX750-D-B ATX12V v2.2 & EPS12V (750W) Case Cooler Master Centurion 534 RC-534-KKN2-GP Mid-Tower Cooling Standard Case Fans and Stock CPU Heatsink Hard Drives Western Digital 1 TB Caviar Black Edition (7200 RPM) SATA
Hitachi Deskstar 500 GB (7200 RPM) SATA
Samsung SpinPoint 400 GB (7200 RPM) SATA Internet Speed 7.1 Mbps Verizon DSL
It's only Vista and Windows 7 (and Office 2010) you can switch between versions (and languages) with the same key. You do not key one key to 32bit and one key to 64bit. All keys is the same.
Remember, that if you buy the full retail version of Windows 7, you don't get TWO keys, so you can't run 32bit on one computer and 64bit on a second computer. It's only possible to have one active computer with that key.