I was jumping systems and decided to /givemoney to someone while the level was loading. Upon jumping into my target system, I found out that I couldn't get out of the chat screen, and any key I pressed would be entered as if I were trying to chat. Consequently, all controls were locked out, and I couldn't press escape to try and reset. I ended up having to force quit Vendetta (OS X - 10.3.5) and start over. Anyone else experience this?

Yes, happened to me once (and I reported it as bug), but, alas, I could not reproduce it... and I don't know what exactly triggered it in my case. /logoff worked for me, though.
OS X 10.3.4

you may have hit ~ which brings up the console, the only way to get out of it is to hit ~ again (additionally you can execute commands like /logoff, or /terminate from there so you shouldn't get stuck).