Adding a router.

more info. but here i go anyway.
1 router should be ok unless that router is used between multiple sites and another is needed for internet access. but there should be a free port on that router to connect the internet connection. also, ip addresses will be an issue.
if this does not help, please add more info.

Your network structure sounds fine in regards to your router. I assume that the T1 connects to your ISP on the internet side, and into your Cisco 1605 router on your companies side. From there you connect into a switch, and the switch connects to various hubs in other rooms, which connect to the users PC's. The router is not an issue. Here are some things to think about.
1. Is your internet connection slow now with the current users? If so you need to look at more bandwidth (another T1?)
2. What is your network structure? Are you running ethernet? 10MB or 100MB? How many open ports do you have on your switch/hubs? Are any of your cable runs over 100 meters?

The more people you add to your network, the slower it will run as users fight for bandwidth. Make sure your switch and hubs are running at 100MB. If your running 10MB, moving to 100MB will speed you up considerably. Make sure you have enough open ports on your hubs/switch to accomidate the new users. If you have more specific questions, let me know.
Good luck!

The 1605 will handle the T1 jsut fine, however as was mentioned, if the internet is slow now you may want to consider additional bandwidth. It is possible to bring 2 T1's into a router ( preferably something a little heftier than a 1605) and load balance between the two. I have done that on a 2500.
The number of clients the router can support will also depend on what the need the internet access for. If it is for major Web development with a lot of up and downloading then a heftier router would also be advisable. However if it is just for browsing then that should be sufficient. To change the IP address on the router do the following:
get the router into enable mode
type the following:
config t
int e0 (can either be E0 E1 S0 S1 depending on the type of interface)
ip address x.x.x.x x.x.x.x
(address)(netmask)
press CTRL-Z and type copy run star

more info would be helpful, feel free to email

Hi...

I think, the hardware is enough. there is no need to buy the extra router. but still it all depends upon the traffic to the internet. If the traffic is almost same e.g. forms/drafts that are downloaded day to day that time, its better to use caching product.

in case, if you required more clarification pls let me know.

vinod