how to upgrade a debian system not connected to network

["J.S.Sahambi" <jsahambi@iitg.ernet.in>]

I have a two debian/unstable systems (let us name them PC-A and PC-B). 
Both have got different packages installed. PC-A is connected to 
internet with 2 MBps link and so there is no problem in upgrading it 
regularly.

PC-B is not connected to internet. So I whenever I need to upgrade the 
system I download the 5 CD's of sid form 
ftp://ftp.fsn.hu/pub/CDROM-Images/debian-unofficial/sid/ ,
burn then in RW-CDs and then upgrade the system.

I want to know is there any method by which I can download the packages 
requiring upgrade for the PC-B in PC-A (remember PC-A and PC-B have 
different list of installed packages!)?

If I can do that, I can copy the .deb files to  /var/cache/apt/archives 
of PC-B via a portable usb-dsik and execute apt-get upgrade.

Any help will be appriciated.
Thanks
JSS