I assume you mean Cisco 2600 series router running IOS 11.3, and not Cisco's Catalyst 2600 Token Ring switch.
Which model 2600 router do you have? And what feature set on the IOS? Do a "show flash" and see what IOS image file(s) are on the router.
Routing IP between 2 VLANs is possible with the plain old IP IOS if you have at least two LAN interfaces on the router; so the model would have to be a 2611, 2621, or 2651. Each LAN interface would plug into one VLAN access port on the switch. This is a "multiport router" setup.
Routing IP between 2 VLANs is possible with IP Plus IOS if you have just one LAN interface on the router; so the model would have to be a 2610, 2620, or 2650. (Not 100% sure about the 2610; but I know for a fact that the 2620 and 2650 can do it, because I've done it.) The LAN interface would need to be configured to support subinterfaces (which is what requires the Plus version of the IOS). The switchport that it plugs into on the 2950 would need to be defined as a VLAN trunk port (802.1Q trunking). This is a "router on a stick" or "one-armed router" setup.
Probably you should look at upgrading the IOS release to something newer than 11.3. It may be that support for LAN subinterfaces wasn't introduced until 12.something.
If you have to upgrade the IOS release and feature set to IP Plus, then you will probably also have to upgrade the router's flash memory and DRAM memory as well. All those costs add up; it may be cheaper to just buy another switch, one that can do Layer 3 routing. A low-end Catalyst 3550-24-SMI which can do basic IP routing (static or RIP) at wire-speed, easily outperforming the fastest Cisco 2600 series router. A Cat 3550-24-EMI can do advanced IP routing (OSPF or EIGRP) and IP Multicast routing, also at wire-speed.
Hope this helps.
