wanderer are you sure it creates a "windows.old" file for a 32 bit to 64 bit change? i know it does that if you upgrade from one os to the next (7 to 8 for example), but i thought for a 32bit to 64bit change you had to reformat and start over. I could be wrong though, just had to ask, rather be safe than sorry.
and kebab, the best way to really ensure you dont lose files is to back them up on an external drive and restore after you finish the install