Yeah, relax, you should be OK, assuming you didn't overwrite all your info. IF you did, like you said, the worst that will happen is you'll need to reinstall winbloze.
That's why we need to see what your fdisk -l output is, and then to also verify what's getting seen during the install/boot time with /etc/fstab
Hopefully you will still have a fat/ntfs partition (which fdisk -l will tell us) and then we will simply setup your bootloader to show it at boot time.
Some ways to find out what bootloader you used, see if you have LILO installed on your system:
locate lilo (after running updatedb)
Anyway, if lilo is there, and there is an /etc/lilo.conf file, I'd guess it's lilo (and I hope it is
since that's all I know how to work with)