I had the exact same problem yesterday, it took me a few hours to find the info (the irony - bootmagic screwed up windows so I had to use linux to find out how to correct it!).
Im at work at the mo so I dont have the link to the pages where I found the answer to your question, but basically I downloaded a small program called BootIT NG. It's free for the first 30 days but it turns out you dont even need to install it!
The easiest way is to download the program [http://www.terabyteunlimited.com/
] read the read me (or bits of because its long and complicated and confusing), create the bootit ng floppy disk with the bootit.exe (i think that was the file) and then boot your computer from this floppy.
I didnt want to enable greater than 4 partitions and I cant remember what i answered to the next question, but after these a window comes up that allows you to view your hard drives and your partitions.
Now I know Im going on quite a bit (its still a little scrambled in my head!) but the ntfs partition needs setting to 'active'. You'll find the partition is currently set to 'hidden'
Active is number 7/7h I believe and the hidden was something 17.
Anyhow, that should sort it, I hope I havent confused you even more.
I'm off to try and solve another problem Ive made myself!! I never created a user and was using root, then I changed to use kde and it comes to a linux.host login and wont let me log in as root - they problem is because i dont have a login for any other user I cant now get into linux!!!
Edit - Sorry, I was making assumptions I probably shouldnt have - I already had grub installed and it was all previously working (I could boot into either windows or linux). The autochk problem is usually because it cant see the ntfs partition. It was bootmagic that caused my problem in the first place (trying to use it to boot from windows straight into linux - never again!!) but i dont have a disk.
Let me know how it goes.