If you do a clean install of W7 into the space previously used by Vista and the recovery partition (use "custom" options at the beginning of setup to enable deletion and reformat of those spaces) W7 will install with its own BCD (probably into a hidden (unlettered) 100MB partition).
If you want W7 to stay all together in one partition, best use a 3rd party partition manager to reformat that space into a single primary first, then install W7 into it.
Simply add an XP entry to that BCD (auto) to locate XP and give you the dual-boot option.
If you want W7 to stay all together in one partition, best use a 3rd party partition manager to reformat that space into a single primary first, then install W7 into it.
Simply add an XP entry to that BCD (auto) to locate XP and give you the dual-boot option.