Hello,
i was having win 7 installed, but now i have one more hdd with xp installed as primary drive. Can i have the os win 7 too? if so, should i have to change my primary drive to win 7 hdd?
Since both OS's are preinstalled, I think you can use bcdedit to update the boot loader/menu. You can export your current settings first so that you can restore them if you make a mistake.
There is a free version of EasyBCD available to non-commercial users - you just have to look to find it.
All the way at the bottom of the screen - Just under the blue Buy Now button.
"Download free for limited, non-commercial use"