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.
If you buy a newer machine, you have got the same chalenge. But it's an assumption as to how incompatible your accessories are in the first place.
I just went for the newer machine and waited to find out what didn't work and ended up replacing only a scanner.