Hello Toast.
Firstly, I'm not the only one who runs these forums. Oddworld Forums are a joint project between both me and Abe Babe. Just wanted to clarify that there are two of us, in case you weren't aware.
Regarding your question, I'm sorry to say but as far as I know, Geocities doesn't allow a UBB to be installed. I don't even think they allow you to place customized cgi scripts on your account. Also, setting up a UBB isn't just uploading files. You have to set different file and directory permissions. Unless you get a server that allows it, you wont be able to set up a UBB. In the mean time I suggest you get a board at
www.ezboard.com, which is quite a good service despite the excessive advertising. Good luck!