Adding fake entries or some hidden keystrokes are NOT secure. If you don't want someone to boot Windows on your computer, then adding protection only for newbies is not sufficient. I can't imagine a case where you don't want to protect from experienced people, but only from newbies.
As a solution, I would password protect the bootloader (you use GRUB2, right?). It will allow you to protect specific entries, so it will require a password to boot Windows, but it won't require a password for any other entries (Ubuntu, Debian or whatever). There is an excellent HOWTO on the Ubuntu Wiki.
NOTE: this still doesn't stop a prepared person from booting a LiveCD, retrieve the bootloader password and boot Windows. To prevent this, you have to add a BIOS password and set the HDD as the first bootable device in your BIOS. You may want to read further on physical security. There is a good HOWTO on it on TLDP (the bootloader section is a bit outdated, refer to the wiki page I linked above).