If you do an in-place upgrade from 32bit to 32bit, you lose nothing. Moving to 64bit requires a clean installation, which means the drive will be formatted and you need to make backups.
NO. Upgrading to x64 from x86 will indeed require a clean install, but the old installation will be bundled up as windows.old and all the files will be available for use. Not the paid programs though (Office, Photoshop, Metastock, whatever).
And this, if you install on the same drive. Installing on a different drive will not affect your current installation one bit.
And if all you got is upgrade media & you wanna duel boot, there are many tutorials on the net that lays out "How to clean install from upgrade media"?