he's done that and now his mouse is arsed. to be honest i think it's better to edit XF86Config by hand because of two reasons:
1) xf86config does not have questions relating to every possible section of a modern XF86Config file
2) when editing by hand you can change one section eg only the mouse section and not have to generate an entirely new file.
for that mouse thing, just open up your XF86Config file in a text editor and find the mouse section, now using the man page of XF86Config, edit your mouse section (probably the driver line) so it works, then save, then restart x. the driver is probably PS/2 but i hear it should be IMPS/2 which does the same job as PS/2 but with tons of other stuff too (like it can drive USB mice, and some funny nonstandard ones et cetera too)