Creating an article
Please consult Editing and Text formatting.
OpenOffice 2.3 has a MediaWiki export filter, so you can use OO Writer for formatting and then export that.
generating a box of source code (e.g. to show a script or input file for a program)
Simply introduce a blank at the start of a line. To avoid interruptions of the box, empty lines must start with a blank as well. Example:
shelxc pulg<<eof INFL D22-ip.hkl HREM D22-rh.hkl CELL 85.71 85.71 145.34 90 90 120 SPAG P6522 MAXM 2 eof