i can't say specifically how other OS's are detected by most linux installer, other than that they are detected pretty reliably. What I CAN tell you is that they most reliable thing, hands down is to install the bootloader to the MBR. You can use /boot but thats a legacy thing, and more work.
You can choose not to install GRUB or LILO, but then you'll need to get the windows bootloader to recognize and boot linux. I have done this, and its a tremendous amount of effort for no good reason. You gain nothing. I can't think of any situation where you would HAVE to run the windows bootloader, but if you did, thats where its useful.
Bottom line: always install either LILO or GRUB to the MBR and your life will be easy
