Acronis Image 8.0 and network/partitions

I have bought a 160MB USB hard disc which I want to use to regularly image my desktop computer and my laptop computer which will be accessed over the network.

Both computers run Windows XP professional. My desktop hard disk is divided into three partitions by Partition Magic, the first partition is the active partition and contains data and programs as well, and the other two partitions contain data and programs for photos and music respectively. My laptop simply has a singly partitioned hard disc.

Despite reading the manual and forums, I still have the following queries:
1) is it possible to do what I want to do using Acronis Image running from the desktop and accessing both the desktop and laptop?
2) should I do anything to this USB hard disk apart from simply formatting it? Do I need to partition it before I image the two computers? If so I have no idea what size to make the partitions as I cannot work out what size the images will be.
3) when I repeat my imaging process on a weekly basis or thereabouts, is the entire image recreated or are incremental changes made? What is the quickest way of doing this process on a weekly basis?
Looking forward to your expert advice,
Suzanne

P.S. it seems to me that using the Secure zone is not something that would be helpful for me to do as I do not have lots of hard disk space free on any of the discs actually in my machines.