Hi,
I had xp already installed on my computer first, I merely formatted my 2nd. h-drive and installed win 7 on it, and the choice to boot was there, default win 7 or up arrow for "older" operating system, try a re-install of win 7 to the h-drive, after making sure the xp h-drive is master and the 2nd h-drive is set to slave, you should be ok then