DBP is a BCD editor and not a boot manager as you seem to be under the impression it is. All it does is edit the BCD and whether installed or not the changes you make to the BCD remain in place as that is what Windows 7 uses to boot with...BCD means boot configuration data.
You will have to install DBP in at least one of the operating systems again (I suggest Windows 7) and then delete the XP entry using the Operating Systems page, highlight the XP entry and click on the red X.
Next, again on the Operating Systems page, change the boot time out to 0 (zero) seconds for the Windows 7 entry.
You now will need to check to see that each operating system has it's own boot system files on the root of it's own hard drive so that you are able to boot to the hard drives independently. Copy
(do not Cut) and Paste them to where they need to be. Perhaps this is going to give you a bit of a headache since each drive will need to see itself as the drive tagged system...that is, the drive on which the operating system looks for the boot system files. The boot system files for XP are ntldr, boot.ini and NTDETECT.COM and the boot system files for Windows 7 are the file bootmgr and the folder Boot (plus it's contents of course).
You may also have to run a fixboot and a fixmbr command from the command prompt of your Windows 7 installation DVD and/or your Windows XP CD depending on your drive configuration, but first try the above and we can take it from there.
Back up your BCD using the Care Center page of DBP before you do anything so that you can restore it if something goes wrong. It's best to save it to the root of one of the drives so that you can find it easily without having to wade through a lot of folders to find it if you have to.