Okay, so the problem has nothing to do with variable collisions. Quite simply, whatever that script/software your using is doing something rather stupid and probably dangerous too... None of the mysql query functions specify what database connection to actually use, so it just defaults to "the last one used." As the newsbox does SQL queries, your scripts start trying to lookup info in the XN user database after it's included, rather than your own database. That's not something that's going to be fixed by w3c valid css or other fix to the newsbox. The "SomeryC" scripts you're using are simply coded in a poor way, much like the newsbox variables were. I've rewritten that side of things, but you'll have to rewrite the other side to fix this.
The one other option is to make a separate page, with nothing but the newsbox on/in it, then include that as an iframe on your real page. If you do it right, with no scroll bars or anything, it'll look just the same. That's probably the easiest solution for now. The new newsbox is several months off at least, and I'm still not decided on exactly how it'll function, or what resources it'll use. That is to say, I don't know if it'll have this same problem or not. I don't THINK it will, but we'll see once I get more ideas solidified for it.