I have Windows, and 3 different Linux's all on the same hard drive, and it all runs quite smoothly. You do not need any "startup disks".
Most newer versions of Linux use GRUB (Grand Unified Boot Loader). If you want to dual boot with Windows, then Windows MUST be installed first, and Linux second. During the Linux install, allow GRUB to be installed in the MBR. You can then use GRUB to boot either Windows or Linux.
I use a 3rd party boot loader (Acronis OS Selector) because I find it easier to manage more than 2 OS's.