It is a PITA.
Install a 32-bit version, as a mini-OS to bootstrap yourself into 64-bit;
Or, modify the DVD you will burn by editing the ISO, which can be done with VirtualBox etc.
I did it multiple times and posted a long rambling thread over on Boot Camp AD.
It is weird.
For fun, I install W7 x64 on PC, moved it over to Mac Pro and Windows gracefully just updated all the needed chipset drivers for me.
As usually, there are multiple ways to do anything.
Pull Mac drive and system, install a RAW drive or format as MBR and MSDOS, you'll want 3-4 partitions or multiple drives.
By using 32-bit version, you can then create a couple volumes.
8GB for editing the ISO and DVD or to run the installer from. This is a very fast way to do any install. Same idea works with Mac OS and restoring the DVD to disk.
When you burn Win7 DVD, do so at slow/reduced speeds.
20GB for first Win7 32-bit partition.
Whatever you want for x64.
Data volume?
A 64-bit can't be installed over 32-bit, but it will install to another volume all while you are booted into Windows 7 x32.
It took some playing around.
Modifying the ISO with a Windows utility worked, once but I never got the hang to do it again, kept getting unbootable copies and wasted DVDs.
Intel has UEFI 2.3 as the latest and I have been tempted to become EFI Group membership just to nuke the olde EFI32 - I now work mostly on a pair of i7 machines running 7.
