Files with the .bkf extension are files backed up using Windows Backup Utility (located in Programs→Accessories→System Tools); must be installed from the XP Home installation disc to be used with Windows XP Home Edition.
I assume you backed up from the XP operating system. Windows 7 will not support the .bkf extension.
Go to heading "How to Restore BKF Files in Vista after Switching from an Older Version to Vista?"
According to http://www.bkfrepair.net/
you can download and try the program for free.
NOTE: I have never used this program, so I can not speak to its functionality.
It does seem to say it can do what your need. Good Luck.