I have had good luck in the past with the Ituner Spectra8, a four-chip card.  Been able to get 5 fps out of as many as 12 cameras (3 boards) simultaneously, and came oh-so-close to 16 cameras at the same rate before I got mad at the VIA motherboard in use (it did love to throw PCI bus errors and blue screen once I upped the ante to 16 cameras - no matter how much I hacked Motion apart and forced independent threads per camera for anything that hit any bus and coordinated all bus access via mutexes/semaphores and..and...). 

Then that project ended.  Good thing - working with bad hardware makes ya nutz.

john bray said the following on 3/26/2009 2:08 PM:
On Thu, 2009-03-26 at 08:40 +0000, Pall Thorsteinsson wrote:
Thanks for your inputs Stephen, Bill and Jtd.

jtd: I was thinking more of a card that has Hardware compression. Even 
though I think the computer could handle it, I belive HC would be more 

Solving one problem will always create others, so movement is something 
we will have to deal with later, its just good to know it can be dealt 
with. :)

hi pall -

there are lots of video cards that work.  what you want to be sure of is
that there is one video chip per camera.  one of the common chips is
bt878  or bt8xx.  some boards have only one of them.  others have 4 or
8.  if you are wanting to run at full pal speed, you will need a board
with at least one bt chip per camera.  a board that has to switch the bt
chip between video streams will allow only very slow frame rates.  many
of us use and are fond of the kodicom boards.