yes you can do what you want .
just put the win64 disk in the drive and boot from it ...when asked where to install to type in the drive letter of your second drive.
easy as that...once windows has finished installing and you restart your pc ,you will get a menu asking which operating system you want to load .
one thing you should be aware of though, there is not a lot of drivers for 64 bit windows as yet.
so check for drivers for all the items you need to use,printer,scanner, graphics, sound,modem and so on...before you install 64 bit windows.