"Kept back" packages?

[Try KDE <trykde@rogers.com>]

Hi,

I have a pre-woody installation:

# uname -a
Linux bigbird 2.4.18IP #1 Sat May 4 18:39:41 EDT 2002 i586 unknown 
unknown GNU/Linux

# apt-get -v
apt 0.5.4 for linux i386 compiled on Aug 19 2001 01:02:26

When I do a "apt-get upgrade", there are a lot of packages "kept back". 
How can I find out why they are kept back, and how to "unleash" them?

Thanks,
-tk