you can use grub manually from the command line when you see the splash screen press c. that will take you to grubs command line. then if you know what partition you have what on you can do the following to boot backtrack.
grub> root (hd0,0) #if its on your first hdd if not (hd0,1) etc
grub> kernel /vmlinuz root=/dev/sda3 rw vga=0x317 #use your partition
grub> initrd /initrd.gz
if you not sure use find stage1 and play around with different partitions.