Hi,
Firstly make sure you have Catalyst 2950 Strong Cryptographic (3DES) Software on your switch
You need to create a domain name first on your switch
ip domain-name
Then you create your private key
crypto key generate rsa 1024
Once complete you can then SSH to the switch.
You can disable telnet on your VTY lines by using
line vty 0 4
transport input ssh
HTH
PD