Click here which is similer quetion.
a) Option 1:
1) Insert the Windows 7 DVD into the CDROM.
2) Shut down the computer. (DO NOT RESTART)
3) Start the computer, & immediately after that start tapping on F12 which will give you boot options. Select CD/DVD ROM Over there.
4) Windows 7 should start the installation Process.
b) Option 2:
1) boot the system normally using Ubuntu installation that is there on Hard Drive.
2) Once you reach Ubuntu Desktop, insert Windows 7 DVD in DVD ROM Drive.
3) Ubuntu will automatically give you pop-up of the Windows 7 DVD & Start the Default auto-run program of Windows 7 DVD.
4) Click on the option to install Windows 7 from that pop-up menu.
System may restart Automatically After step no. 4
5) Windows 7 will start the installation.
Let me know if u have any further queries.