Most systems will allow you to install whichever configuration you boot to on the Install Media. The Windows 7 DVD and most flash drives have 2 boot images, one for UEFI and one for MBR. If you see the MBR option in your boot device menu, you should be able to boot to it and install in that mode.
If you can't see the MBR Install version, you may have to change a setting in the bios to allow your system to see the non-uefi options.
When you try it, let us know exactly what happens.. maybe we can recognize the symptoms if the install doesn't go smoothly.
Well, 32-bit Windows will run on UEFI based platforms - it just cannot support UEFI's advanced features. Note that most UEFI implementations support CSM (compatibility support mode) which emulates regular BIOS. As noted in this Microsoft white paper "UEFI and Windows",
UEFI isn't specific to any processor architecture. It can support modern 32-bit and 64-bit firmware device drivers. The 64-bit capability enables the system to address more than 17.2 billion gigabytes (GB) of memory from the earliest stages of boot.
Note: The 32-bit editions of Windows don't support UEFI features. Only 64-bit editions of Windows can take advantage of the features that 64-bit UEFI firmware enables. Fortunately, the CSM in current UEFI implementations enables 32-bit operating systems and other operating systems that don't support UEFI to boot on hardware that has UEFI firmware. But, operating systems that require a CSM to boot can't use UEFI-specific features because the CSM emulates earlier BIOS.
Still, the advantages of UEFI over BIOS are significant. And the advantages of 64-bit over 32-bit are too. So the best solution for the vast majority is to use 64-bit Windows on a UEFI platform - if possible.