You should be able to get the dual boot working like this:
Copy and paste ntldr, boot.ini and ntdtect.com from Xp partition onto 7 partition.
In Disk Management , mark 7 partition Active.
Boot 7 dvd and run startup repair 3 times.
7 will now be the System partition.
Add XP entry to bcd .
It doesn't solve the mystery of your physically disappearing Boot folder - but it shouldn't also happen on the 7 partition.