I want to Share My A600 USB Cricket Broadband internet Connection on my linksys wireless router. I have a mac running Leopard.
If I understand it, you are trying to do this:
Internet --> USB Modem Stick --> Router --> Mac(s)
This would probably be the best solution. It would replace your Linksys router. These devices are designed specifically for what you are trying to do.
This is a similar product with ethernet ports ,linksys e2000 review.
Netgear also makes a wireless router with a USB port for a 3G modem but I haven't heard things about that one.
Here is the link to the Netgear one, but I personally wouldn't buy it.