Hmm, thats a different one. I've seen issues before with USB devices causing intermittant keyboard issues, but if thats the case, you would be seeing that everywhere, even as you were typeing that post. I'd suspect a macro or something broke in a recent patch and is misfireing, or possibly a cirrupted game installation. Maybe try a full file scan from the patcher?
Is there any chance something is hitting one of the function keys or something towards the edge of the keyboard that would be hitting with both keyboards you tried, but wasn't there before?
To verify it isn't the actual hardware of your machine, open somethign like notpad or word, and leave the keyboard curser in it for a few hours overnight and see if any random letters show up. If not, then its almost certanly your everquest installation.