[Arm-dev] Making an image

Can I have a little help making an image via dd, and then compressing it?

I want to save 'checkpoints' of my build process, so that when I have to 
go back, I do not have to go all the way back to the base image.

I have built my basic image (I will be updating my howto, found a few 
bugs), and fdisk reports:

Disk /dev/sda: 120.0 GB, 120034124288 bytes, 234441649 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x0000c89d

    Device Boot      Start         End      Blocks   Id  System
/dev/sda1            2048     1026047      512000   83  Linux
/dev/sda2         1026048     2074623      524288   82  Linux swap / Solaris
/dev/sda3         2074624     6268927     2097152   83  Linux

Obviously, I do not want to dd the whole 120GB, as I am still only using 
4GB, though I will probably have to enlarge sda3 a bit to hold all the 
software I need.  I did this a couple years back, but can't find my 
notes.  :(

thanks