Physically you have several possibilities: if you currently have a WIC-2T, you can add a second one or replace it with a NM-4T; if you have 2 WIC-1T's you will need to replace them with 2 WIC-2T's or a NM-4T.
Apart from that, there's the routing issue. What is on the other end of the T1's? How is routing currently done?
To replace a static default route to the Internet, you can implement PBR (policy based routing) on the fastethernets to route traffic coming from f0/0 via multilink1 and traffic from f0/1 via multilink2.
E.g. create an acl that matches all traffic from noc to internet; then create a policy map that sets link1 as the nexthop for traffic matching the acl and apply this policy to f0/0. Similarly for f0/1 and link2.
You would have to check if the 2651 is performant enough to do PBR at 6Mbps, you will want to enable fast-switched PBR, see http://www.cisco.com/univercd/cc/td/doc/product/software/ios120/12cgcr/qos_c/qcpart1/qcpolicy.htm
Of course if you already talk some routing protocol over the current link, it's a whole different issue, you'll probably want to combine PBR with selectively advertising routes with routemaps (only advertise the NOC network via link1 etc.).
But maybe a different solution altogether is to combine the 4 links into one multilink and do some form of QoS to prioritize the Noc traffic?
hth (let me know if this is not clear or if this is not what you meant)
Herbert
