Is the 'latest version of fluxbox for SuSE 8.2' the latest stable version (0.1.14) or latest development version (0.9.4)?
Version 0.1.14 uses the bsetbg command, version 0.9.4 uses fbsetbg. Either of these will be put in one of two (that I know of) locations:
in the ~/.fluxbox/init file like this:
session.screen0.rootCommand: bsetbg /location/of/picture.png
or in the style file itself like this
rootCommand: bsetbg /location/of/picture.png
If you set the BG in the init file with the -f option, the BG will not change, no matter what style you use.
Read the documentation at the Fluxbox site: http://fluxbox.sourceforge.net/docbook.php