I see a lot of dd related questions, but could not find answers to the following. If question/answers already exist, please point to them, then flag to close, delete or merge.
- Can a working linux installation (say on 
/dev/sda7) be cloned to an external hard disk partition (say/dev/sdb2), while on it? (/dev/sdbis a 1TB USB hard disk,/dev/sdb2is of size 100GB) - If not, can I do it using a live cd? Will the cloned partition on external drive be bootable?
 - If it is not bootable, how to do that?
 
Why want to do that ? : Need to carry the cloned external drive than the laptop itself, with all the installed (& customized) programs and data.
Additional info (relevant parts only):
$ sudo fdisk -l
Disk /dev/sda: 160.0 GB, 160041885696 bytes
Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        2550    20482843+   7  HPFS/NTFS
/dev/sda7            5660        6904    10000431   83  Linux
$ df -h
Filesystem            Size  Used Avail Use% Mounted on
/dev/sda7             9.4G  7.4G  1.6G  83% /