Try wireshark.On FC8/9, use yum to install wirkshark and wireshare-gnome. A wireshark icon will be created under "Application->Internet->Wireshark Network Analyser". Launch the program and run under unprivileged mode. Click on File->Open to open that tcpdump file. Look for the first "telnet" packet and highlight it. Click "Analyze->Follow TCP stream" and you should see a new window pop up and should it will show you your telnet session in clear text, including your the user name and password.