[praka123]

from livecd,launch "gparted" and make ur "/"(install partn root) to the size u want.and dont make swap of 1GB,it is a waste.prepare ur swap partition around 400-500MB maximum.after preparing and formatting partitions as above,open a terminal from applications>accsries>terminal and run "sudo ubiquity" to start the installation.during installation,select manual partitioning and show the installer the partition and swap u earlier made using gparted.
Ubuntu installer seems a lil problematic sometimes.so do as above.