After downloading bt4-final.iso, md5 checksumming it, booting the KDE desktop and using the install.sh provided on the desktop, I'm attempting to install Backtrack 4 Final to my Macbook 2,1 hard drive on sda5. I want to install the grub bootloader to sda5 as well, since want to retain my current rEFIt bootloader. So far, doing this on sda3 with Ubuntu 10.04 works great, but Backtrack fails every time at the grub install step.

My partition scheme:
sda1: 209 mb boot partition (for the mac EFI boot)
sda2: 59284mb hfs+ (Mac OS 10.6)
free space 134mb
sda3: 19999mb ext3 (Ubuntu 10.04)
sda4: 29999mb ntfs (Windows XP Pro)
sda5: 7999mb ext3 (for Backtrack 4 final)
sda6: 2406mb swap

I configured the partitioner to load sda3 as '/Ubuntu', sda4 as '/WinXPPro' and sda5 as '/'.
Then I configured the boot loader to be installed on '/dev/sda5', because I want to retain my current bootloader setup.
It failes at 94% at "/dev/sda5 grub-install".
The effor message is as follows:

Installer crashed
We're sorry; the installer crashed. Please file a new bug report at https://launchpad.net/ubuntu/+source/ubiquity/+filebug (do not attach your details to any existing bug) and a developer will attend to the problem as soon as possible. To help the developers understand what went wrong, include the following detail in your bug report, and attach the files /var/log/syslog and /var/log/partman:

Traceback (most recent call last):
File "/usr/lib/ubiquity/bin/ubiquity", line 229, in <module>
main()
File "/usr/lib/ubiquity/bin/ubiquity", line 224, in main
install(args[0])
File "/usr/lib/ubiquity/bin/ubiquity", line 68, in install
ret = wizard.run()
File "/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py", line 437, in run
self.progress_loop()
File "/usr/lib/ubiquity/ubiquity/frontend/gtk_ui.py" line 831, in progress_loop
(ret,realtb))
RuntimeError: Install failed with exit code 1
Traceback (most recent call last):
File "/usr/share/ubiquity/install.py", line 2112, in <module>
install.run()
File "/usr/share/ubiquity/install.py, line 428, in run
self.configure_bootloader()
File "/usr/share/ubiquity/install.py", line 1599, in configure_bootloader
"GrubInstaller failed with code %d" % ret)
InstallStepError: GrubInstaller failed with code 1

Please help!