If you research this you should learn that if you did have a dual boot and wanted to remove the older os you discover there is no supported method that always works to get it done. And you would learn that you install from oldest to newest OS to get the dual boot (without changing the BIOS.)
There is a scenario that doesn't work at all and that is on some boards when IDE EMULATION is turned on.
Try to live with your setup and you may find you use 7 exclusively.
I have installed Win7 on my Sata drive that use to have Win Vista. I figured that installing Win7 will give me a dual boot system, but it has not yet. In order for me to have dual boot I end up going into CMOS and changing which drive is first and which is second. Which one if first will boot up to that operating system.
Any ideas of how I can have a dual boot system with the Sata drive having Win7 and the IDE drive having WinXP system. Would appreciate any ideas.
I tried when I had Vista and it did not work for me.