Yes you could it. Linux (For example: Mandrake) have in it's installation an option that permits that you install linux with a Hard Drive with Windows. At end, you I'll have a Boot loader Interface called Lilo that show you what OS you will use. Also, you could share files between both OS (Only if you have a software that support NTFS installed in Linux).
Also, you could install Others OS in your additional hard drive not only Linux (Mac OS, FreeBSD, Solaris, Novell, Win98, ME, W2K..)
You just only have to assure that the boot interface be rigth configurated.