All windows installers (at least the ones that I've used from 3.1 to Win 7) install their own bootloader if one is not found (and of course, it does not recognize Grub or Lilo).
What you need to do is reinstall grub, by booting up linux somehow (live CD, the install image, or a USB install. It doesn't matter, really), and run this command:
If your primary harddrive is not
sda, then substitute that device node with whatever is appropriate.
sda corresponds to the first SATA drive in most cases, so if it is your primary or only drive, then it should work for you.
grub-install will probe your drive for any bootable OSes and install Grub with an appropriate OS list to choose from.
Setting the timer for OS selection is done by editing
/etc/default/grub with your favourite text editor, and adjusting the line that says