You can try google for the super grub boot disk, this will let you boot the backtrack partition if it is still intact. At which point once you have that going you can reinstall grub to the mbr and get it to regenerate the grub menu.lst config file which will at a minimum get you booting into backtrack again, without the super grub boot cd or USB. Once you have that you can manually add an extra entry to your menu.lst file to chainload the windows 7 partition.
There are heaps of threads via google for doing all this I know because I have used them for all the times I have botched grub and the boot process. It is a great learning curve you learn lots by breaking and fixing them