There is an alternative boot method to the official one posted on the "How To" as follows:
1. install WIN 7 for the first (it will create its BCD bootloader)
2. leave or (free up by shrinking etc) a large enough unallocated space on the drive (continuous free space!), very minimum 9-10GB but if you will want to install larger apps than increase it
3. boot the PC from a BT4 R2 DVD to start installation
4. choose any of the offered load options (Graphical or command mode etc)
5. BT4 partitioner will load and there you have to choose the "Guided, use the largest free space" option for installing BT4
6. VERY IMPORTANT (if you do not want the orginal MBR/Win bootloader being touched/modfied by BT4/GRUB):
Before you would click on the last "OK" there is an "advanced options" -or named something like this- button on the screen where you HAVE to select "install bootloader" not onto the main partition (WIN7 neither its 100MB system reserved partition) BUT choose the free partion for this to where you install BT4 (not its other swap file partition which has been automatically created by now)
7. After BT4 has been installed fully (run install.sh from BT4 desktop), you need to reboot and Win7 will boot now. Install EasyBCD from the web and using this app add a new entry to the Win multiboot section (named as you wish ie BackTrack or so), click SAVE, than OK.
Reboot and you will be offered the multiboot choice.
Following this GRUB bootloader will not touch the original MBR or WIN BCD loader, so that I think so you might not have any problem with Bitlocker (I did not try Bitlocker), but I use this dual boot system and it has no any problem (without Bitlocker).