If your going to lock pixels I would suggest locking at around 800 simply because you can never be too sure of who's viewing your site. I think right now the average resolution is still 800 x 600. All of my sites are locked at 800 and it loox good at all resolutions IMHO. My screen resolution switches between 1280 x 960 and 1280 x 1024 (software dependant) and the sites still don't look too cluttered.

I'll do what I can but I am no phpnuke hax0r so you may be stuck with simple theme alteration, block removal and a few other goodies. I answer questions based off of my understanding of phpnuke as a webmaster and someone who alters themes. I have never created a theme personally and wouldn't have any idea of where to start should I try.

Just so you know, I'll do what I can but I'm by no means a miracle worker.