just pop in the live cd or usb for the linux and follow the on screen prompts to the point where it gives you the option to manage the installation on the harddisk yourself if you choose the default it will erase any existing installation so be careful about it, also the LILO installer for Linux is very user friendly and you can partition and allocate sufficient space without any problems yourself just be careful if you don't want to continue with linux any more and want to delete the linux partition it will corrupt the Master Boot Record and you will need a Windows disc to correct it using the Fixboot and fixmbr commands it's easy just google a lil bit and dive in when you are a bit confident about it cheers.
Hello,how can i allot more space for ubuntu on working dual boot system
shrink your existing windows partition adn that will free up space for Ubuntu
right click Computer, click disk management, when the computer management console loads, under storage in the left pane, select Disk Management and then in the right pane select more actions>All tasks>Shrink volume. It all depends on where your system files are stored that determines how much space you free up.