How to share my broadband pcmcia card to another pc via patch cable

That's called Internet Connection Sharing.  If you right click on the network connection for the pcmcia card, go to properties, there should be a sharing tab.

Here's a little writeup from MS on it:

http://windowshelp.microsoft.com/Windows/en-us/help/bfd3bd31-82f0-4b9c-9cde-fb92bc2b14771033.mspx

You will need to use a null-modem cable and set up basic networking. The networking set-up wizard in "My Network Places" is quite simple to use.

Or, if the two computers have wireless, I think you could set up an Ad-Hoc computer-to-computer network. Never done that as I felt it wasn't secure enough - but it is an option. Again, that's "Set Up Wireless Network  for a home or small office" under "My Network Places"

1st step.   Network the two PCs together.   If they are already on the same ethernet or wireless network then you are ok.   If not you will need to create one.   If both have wireless you can create an ad-hoc network between them.   If not and both have ethernet port then the easy answer is to buy a cheap switch and connect them both.
To share the broadband connection use Internet Connection Sharing.  This article explains how to turn it on. http://windowshelp.microsoft.com/Windows/en-US/Help/bfd3bd31-82f0-4b9c-9cde-fb92bc2b14771033.mspx
You can put a password on the connection sharing so that not everyone can use it.   An example of how to do this can be seen at: http://www.lytebyte.com/2007/02/21/how-to-share-one-internet-connection-with-another-computer-using-vista/   along with more information on ICS.
 

> You will need to use a null-modem cable and set up basic networking

You won't find one in the stores called that. What you want is a ''crossover cable'' to share with just one other computer without adding a switch too, as lostfocus advises; you can also use a regular network cable if you're going to feed it into the WAN port of a router (very do-able too) to share it with multiple devices.

I have tried all what is said earlier, but when I use the ICS or sharing tab it does not recognize the broadband card.