[Venkatesh]

For the purposes of this answer, I am going to assume that your 80GB (current boot and main) drive is an IDE disk, on the first channel, and connected as master. And I am going to assume that the new 160GB disk (the master-to-be) is an IDE disk on the first channel, connected as slave. I am also going to assume each disk is set up with one large partition, the whole size of the disk.

First, backup anything that is important. You can never have too many backups.

Second, download a Knoppix linux CD and burn that image. Knoppix is a LiveCD, a disc that contains a version of Linux which does not need to be installed. If you are familiar with linux, good. It will really help while doing this.

You will need to boot into Knoppix and mount your hard drives. To do that, boot from the CD, open a terminal window once KDE has loaded, and type:

su (switches to root user)
mkdir /1 (makes a directory called 1 in the root area)
mkdir /2 (makes a directory called 2 in the root area)
mount /dev/hda1 /1 (mounts your existing hard disk in /1)
mount /dev/hdb1 /2 (mounts your new hard disk in /2)
cd /2 (move to /2 directory)
tar -cvzf 1.tgz /1 (archive /1 into a .tar.gz file)
mv 1.tgz 1.tar.gz (rename 1.tgz to 1.tar.gz)
gunzip 1.tar.gz (ungzip 1.tar.gz)
tar -xvf 1.tar (unpack that tar file)

The reason I recommend you to use tar rather than a direct copy is simple. You can store that 1.tar.gz file on another computer or a reliable medium, and have a record of your computer which you can restore from in case of disaster. After you are done with the above steps, you are free to swap the positions of your IDE devices. You will need to boot using a Windows 2000/XP install CD into the recovery console and run "FIXMBR", but then the swap will be done.

This is not an exercise to be taken lightly. If you did not understand any step above, do not try it.

Edit: I forgot about Norton Ghost. It should be able to do the whole process automagically. I have never used it and cannot comment on its use(ful/less).