As other people have said, you have to be carful with dual booting on the same drive with Windows. It doesn't play nice with others. To add on though, Linux can access your NTFS (or whatever) systems fine*. You can leave them as they are and access the same data on both systems, though Windows is not capable of reading most other filesystems.

*May require installing a package, but every distro I've tried could out of the box.