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!)?Others may give a better answer. One easy way that comes to my mind is internet sharing. For example, you can buy a router and connet PC-A & PC-B to the router. The router connects to the outside world through the 2mbps link. The LAN enables to share the files between the computers very easy.
I forgot to mention that there is no possibility of ethernet connection between PC-A and PC-B as they are in different locations.
Waiting for other answers. JSS