Hybridize?

<a href="#" onmousedown="changeImages('topevents', 'images/topevents-over.gif'); return true;" onmouseup="changeImages('topevents', 'images/topevents-over.gif'); return true;" onmouseout="MM_startTimeout(); changeImages('topevents', 'images/topevents.gif'); return true;" onmouseover="MM_showMenu(window.mm_menu_0728010700_0,0,49,null,'topevents'); changeImages('topevents', 'images/topevents-over.gif'); return true;">

I haven't used 'code tags' for a good reason.

Note: You need to make sure that where more one statement ( a statement in javascript is terminated by a semicolon ) is put in a sequence; that return [something]; is only ever the LAST statement in that sequence.