Back Track 5 web site is currently unavailable ??????
Up front, I am not sure. However, most Linux OS installs have options to partition your HD format it & install on your selected partition. If Back Track 5 has this, then you should be able to. My OS uses grub to boot my Ubuntu & Win XP (works for Win 7 too). What does Back Track 5 use? If it uses grub then it should work for dual booting.
Clean up your HD before installing. Do a check for errors & then defrag it.
Rather than keeping the restore option for Win, I would think about making a Win disk & also save the Win drivers for your hardware. The drivers are usually on the Dell web site for download but I would get copies anyhow.