Dual Boot Mirror Problem?

[BigMac]

I just recently purchased a macbook that is partitioned so half of the hard drive is devoted to mac and half is devoted to windows, so that when I boot up, i can hold option and choose which to start from. I believe this is called dual boot? anyway, when I mirrored my hard drive to an external drive, it was successful in copying every file (including the windows files), but i just can't start up in windows now, because when i choose to boot from my external drive, it doesn't give me the further option of mac/windows. Is there a way to circumvent this problem by maybe doing separate backups for each partition, or maybe figuring out a way to boot from the windows side of my laptop once the mac side is open? help is appreciated, i don't want to do something unneeded like buying another HDD or something. thanks