Q. I’m willing to try out Ubuntu Linux but my question is Does Linux grub replace Windows MBR? Can I dual boot between Windows and Linux system?
A. Yes when you install GRUB on first partition, windows MBR get replaced. In most cases GRUB automatically adds an entry for Windows XP / Vista so that you can enjoy dual booting out of box after Ubuntu Linux installation.
In case if you made any mistakes while performing Linux installation you can restore GRUB.
I recommend making a backup of all important data / files before making any changes to MBR / file system or operating system or Ubuntu Linux installation.