If you go to the 32 bit version of Win 7 then you should not have any problems. However, some peripherals (scanners) may not work with the 64 bit version - happened to me my with a Canon n670U scanner which Canon do not provide 64bit Win 7 drivers for.
Some software may also be not compatible with the 64bit environment. Check before you change.
Since the principle reason for me to go to 64bit Win 7 was to use 8Gbyte of RAM for some graphics processing, I have plenty of RAM to run a virtual Win XP machine in Virtual Box which sorted out the scanning issue.