THIS LINK will probably answer most of your questions...
I'll answer some here too,
"what is 32-bit mode? is it like compatibility mode? in other words if i install a 32-bit program, can i use it in the 32-bit mode? what exactly is it"
Well, 32 bit programs do run in the 64 bit version. They load in 'emulation' and this can possibly slow down the app, but it may not be apparent to you, see .
The biggest headache you might find is getting 64 bit device drivers, especially for OLDER h/w, like scanners and printers. 32 bit device drivers will not work. Some programs as well might now work or have full function as they use 32 bit built in drivers for h/w access. Many will have comparable 64 bit versions, like most un-installers, disk managers, and partitioning s/w for instance.
MORE ON THIS HERE