That depends on whether or not the originaly 7 BCD store and boot files were on the 204mb OEM partition which is separate from the Recovery partition. Grub likely ended up on the OEM part at the front of the first drive 7 came preinstalled on. The 8 installer upgraded the mbr and BCD store to 8's while adding 7 in as the second Windows.
For restoring the 7 BCD and mbr entries a 7 repair cd or booting live from a 7 recovery disk live if you have one will allow you to run the Startup repair tool a few times to replace the 8 boot entries. 8 still uses the same type of bootloader as both Vista and 7 but is the newer version. Likewise when removing 7 from a dual boot with Vista you would need to run the Vista Startup repair to replace the 7 mbr and version of BCD store.
With a live ubuntu disk you can browse the partitions on Disk 0 to see just where the Boot folder is located which contains the boot files and BCD store(Boot Configuration Data store). That will need to be marked as the active system since the boot files and boot information are located there. The 7 primary will simply remain as a healthy primary partition.
On other premade systems there is no separate 204mb boot parition where the BCD is located on the hidden recovery partition when found at the front of the drive. Once you boot live from a ubuntu or other distro's cd or dvd like Linux Mint or Puppy Linux this is how the boot partition on a 7 machine will look as far as the folders you will find.
Note this is how that will be named when 7 is custom installed while the 204mb partition has an OEM name to it there.