T-1 and TCP/IP Network Interface

I’m having GREAT difficulty with stability of our local network (12 users) and keeping our Cable ISP link up through our Linksys Cable Router. I feel most of the problem is on the Cable provider side, but they are reluctant to admit it. I have 256K bandwidth available with our phone service and am tempted to switch our Internet access from cable to the T-1 line and add a couple more channels for increased bandwidth. There’s already a data port (RJ45) on our telephone gear switchbox that I can access by one PC. What equipment do I need to interface this T-1 data port with my existing network? Is this something best left to the pros or is it no more involved than hooking up the cable modem access?