It's very possible. You'll find some info here:
Both are also available in PDF and plain text.
Basic info: There is only one master boot record (MBR) that can be read by the BIOS on startup, and that is on the first hard-drive. This MBR is the only way to boot from the hard-drive, that is, without having to use a floppy, CD, etc. So if you want to boot "normally" without peripherals, you will have to have a boot manager in the MBR that will be able to start both operating systems.
One way (I do it like this for SUSE and hope to soon for Debian as well) is to keep the Windows boot manager, install the Linux boot manager into its root partition, then transfer the necessary information to Windows and tell its boot manager (in the file boot.ini) about it.
You could also allow Debian to install a boot manager (GRUB, LILO, etc.) and let that launch Windows. I shy away from this approach because Windows sometimes likes to fool around with foreign boot managers and spoil things, although it's a valid approach when you know what to avoid.
I am not telling you more detail on purpose. You should most definitely read up yourself on this potentially complicated topic yourself. Look around before coming to a decision.