Use line vty xxx (xxx being the numerical value of vty lines) in global configuration to set the number of lines to use. line vty ? will tell you how many you can configure but I think its in the hundreds (sorry, dont have a 3600 in my lab to test it on).
There are only 5 VTY lines availalble for telnet access to any IOS router. These are numbered from 0 to 4. You can configure either one or a range of these. You can allow or restrict access to them, however, you cannot increase or decrease how many VTYs you have.
That first post was correct, just type
line vty XX
and the vty's will be added. You will see them listed seperately in the config
line vty 0 4
line vty 5 9
works every time.
Actually it doesn't work every time. On some devices you need the "Enterprise" image if you wish to support more than 5 vty lines.
Here is my source for this info.