[CentOS] two internet connections questions

I have two internet connections. One is a partial T1 of data (and rest 
voice) the
other is business cable. Both connections come into my office into (2) 
centos 5
boxs with 2 ethernet cards in each box. The second ethernet card is 
192.168.1.59 and 192.168.1.1
respectively.

I have all my DHCP settings setup for a gateway of 192.168.1.1

In the event that the internet connection is DOWN (box is fine just the 
cable modem is down)
how do I set things up so I can take advantage of the second internet 
connection?

Thanks for any tips.

Jerry