Debian :: Running Out Of Room In System Partition

I use Debian Lenny in a dual boot system on a desktop computer with a 40 GB hard drive. There are two partitions used by my Lenny installation, one containing /home and one containing the rest of the directory tree, including /tmp. I guess that I could soon encounter problems using kpackage to obtain security upgrades to already installed packages or backing up files to CD; is that correct? I have plenty of space left in the partition containing /home but have under 500 MB left in the other partition (4.1GB), which is 93% full. A year ago I was fine, but the various package upgrades seem to usually add stuff, so I've gradually filled up the partition.

I have looked at the directories in the filling up partition, and there are not really any huge space hogs, just a lot of packages adding up to filling up 93% of the partition. The fattest directories in the almost full partition are
/usr/lib 1.1GB
/usr/share 1.6GB

Installing another Lenny on another desktop (no more dual boot for me!) is now a high priority, and I hope to accomplish that over the next month or two, but until then I am concerned that my current desktop computer may soon become unusable. I guess that if I tried to simply use the linux mv command, as root, to try to move say the entire /usr/share directory to /home/usr/share, I would not only not free up any space, I'd only move the directory itself, which I guess would possibly render various packages I have installed unusuable. Is there any reasonably simple/safe way to do something like this:
1. cp /usr/share to /home/usr/share
2. replace /usr/share files with symbolic links to new locations.