i would not recommend 32bit , as all the 32bit applications can run on 64 bit os anyway . sometimes still , drivers are the problem , but only if u have older hardware .
+2, clean installation is the only way to move from 64-bit to 32-bit. Why do you want to do this? Just as a fair warning, a program designed specifcally for 64-bit windows, will not work on a 32-bit system...