You don't need to waste space. Works with any two networked computers:
on the server: >netcat -l -p 1234 | bzip2 > /mnt/sdb/hda_lappy.img
on the lappy: >dd if=/dev/hda bs=16065b conv=notruc,noerror | netcat 192.168.0.5 1234
This is a bitstream method of backup using compression on a mostly empty 100 GB drive, and yields a 6 GB image file, but I don't think you could mount this image, so it needs to be restored in its entirety, or not at all.
To restore, on laptop: >netcat -l -p 1234 | dd of=/dev/hda bs=4k conv=notrunc,noerror
on server: >bunzip2 /mnt/sdb/hda_lappy.img | netcat 192.168.0.6 1234
where 192.168.0.5 = server, 192.168.0.5 = lappy, 1234 = tcp port to use.
bzip2 uses an error checking algorithm that is machine, and especially memory intensive. If it bugs out, try turning the AC to a lower temp. in the room where the server is, or get some powerful chassis fans.