I just did the same thing for a set of 40 computers and then another
150. As someone so kindly pointed out to me: Clonezilla. Just put the
disk into the drive, start the computer, make sure to have your new hard
drive and your old hard drive attached some how, and then follow the
onscreen instructions.

I used a external drive that I can swap out hard drives on. It takes
about 4minutes to do 50gb. Though it might take that long for smaller or
slightly larger drives too.

You can use it on any version of any os.
You down load it and put it on a cd.
The os version doesnt matter.

I closed XP Pro, 8.04, 9.04 and 9.10 ubuntu systems with it.

Since Clonezilla is it's own operating system it works no matter what O/S
you might be cloning.

I have downloaded iso file for clonezilla. But, I was having difficulty with
selecting the file I want to download. On clonezilla website, the latest version
has 2 download options. One was 1.2.4-28-486 and 1.2.4-28-686. Apparently, I
have got i386 processor. Therefore, which file you reckon I should download or
it doesnt matter? At the moment I have downloaded 686 one.

If the "686" version works, use it, but I suspect you will need to have the
"486" one unless you are running on a true 64 bit CPU.

Your new drive should have come with a software CD. On that CD is software that
will allow you to do this.

I think I would install it as an extra drive and dd from the smaller to the
larger.