Literally. Move your partition over.
I just installed Ubuntu Dapper (flight 4), onto my Dell Laptop [Latitude D510], and the installer will let you resize the existing partition to make room for Linux.
Of course I had enough free space on the drive, and had my fingers crossed the entire time. But the installer perfectly resized the existing NTFS partition and made room for Linux, and after the installer finished I had a nice Grub boot loader dual booting with Ubuntu Linux and Windows.
Sweet.
I heard that Mandrake 10, I believe, had a resize partition option on their installer, but never got a chance to try it. As for Ubuntu Dapper (flight 4) —- I’ve tried it, and yes it does work.
