I don't think this is more of a JS problem, but an HTML instead.
With that said, i'll start by saying that your structure is a mess. Transfer your <html> tag above the DTD (http://alistapart.com/articles/doctype), not otherwise.
Highlighted is deprecated:
<SCRIPT language=javascript>
<!--replace highlighted with type="text/javascript"-->
This part is erroneous:
<body onLoad=<actinic:variable value="PreloadImages" name="OnLoadScript" /> "MM_preloadImages('NAVIGATION_r1_c2_f3.gif','NAVIGATION_r1_c2_f2.gif','NAVIGATION_r3_c1_f3.gif','NAVI GATION_r3_c1_f2.gif','NAVIGATION_r5_c2_f3.gif','NAVIGATION_r5_c2_f2.gif','NAVIGATION_r7_c2_f3.gif',' NAVIGATION_r7_c2_f2.gif','NAVIGATION_r9_c2_f3.gif','NAVIGATION_r9_c2_f2.gif','NAVIGATION_r11_c1_f3.g if','NAVIGATION_r11_c1_f2.gif','NAVIGATION_r13_c1_f3.gif','NAVIGATION_r13_c1_f2.gif','NAVIGATION_r15 _c1_f3.gif','NAVIGATION_r15_c1_f2.gif','NAVIGATION_r17_c1_f3.gif','NAVIGATION_r17_c1_f2.gif')">
1.) I don't think that the value of your onload attribute is correct (80% goes to not).
2.) <body> has no value and name attributes (http://www.w3schools.com/tags/tag_body.asp).
3.) You might want to use this modification:
<body onload= "MM_preloadImages('NAVIGATION_r1_c2_f3.gif','NAVIGATION_r1_c2_f2.gif','NAVIGATION_r3_c1_f3.gif','NAVI GATION_r3_c1_f2.gif','NAVIGATION_r5_c2_f3.gif','NAVIGATION_r5_c2_f2.gif','NAVIGATION_r7_c2_f3.gif',' NAVIGATION_r7_c2_f2.gif','NAVIGATION_r9_c2_f3.gif','NAVIGATION_r9_c2_f2.gif','NAVIGATION_r11_c1_f3.g if','NAVIGATION_r11_c1_f2.gif','NAVIGATION_r13_c1_f3.gif','NAVIGATION_r13_c1_f2.gif','NAVIGATION_r15 _c1_f3.gif','NAVIGATION_r15_c1_f2.gif','NAVIGATION_r17_c1_f3.gif','NAVIGATION_r17_c1_f2.gif')">
P.S, fix your markup errors (http://validator.w3.org/check?uri=http%3A%2F%2Fwww.thesoftwareshop.co.za%2Facatalog%2Findex.html&charset=%28detect+automatically%29&doctype=Inline&group=0) as well as your CSS errors (http://jigsaw.w3.org/css-validator/validator?uri=http%3A%2F%2Fwww.thesoftwareshop.co.za%2Facatalog%2Findex.html&profile=css21&usermedium=all&warning=1&lang=en).
Hope it helps.