guarda è molto semplice

fai un controllo in JS delle risoluzione..se è 800*600 allora scrivi tutti i tag html della pagina asp con però il documet.write del JS..se è in 1024*768 stessa cosa solo ke ovviamente richiami il filmato con la dimensione diversa..
esempio.
<script>
s_width=screen.width


switch (s_width) {
case 800 :
document.write (" <object classid='clsid27CDB6E-AE6D-11cf-96B8-444553540000' codebase='http://active.macromedia.com/flash4/cabs/swflash.cab#version=4,0,0,0' id='centrale' width='640' height='355' align='left'> ");
document.write (" <param name='movie' value='centrale.swf'> ");
document.write (" <param name='loop' value=false> ");
document.write (" <param name='quality' value='high'> ");
document.write (" <param name='wmode' value='transparent'> ");
document.write (" <param name='bgcolor' value='#0099CC'> ");
document.write (" <div id='awmflash1' style='position:relative;'><embed id='awmflash1' name='centrale' src='centrale.swf' loop='false' quality='high' wmode='transparent' bgcolor='#0099CC' width='640' height='355' type='application/x-shockwave-flash' pluginspage='http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash'> ");
document.write (" </embed> </div>");
document.write (" </object> ");
break;

case 1024 :
document.write (" <object classid='clsid27CDB6E-AE6D-11cf-96B8-444553540000' codebase='http://active.macromedia.com/flash4/cabs/swflash.cab#version=4,0,0,0' id='orologio1024' width='868' height='525'> ");
document.write (" <param name='movie' value='orologio1024.swf'> ");
document.write (" <param name='loop' value=false> ");
document.write (" <param name='quality' value='high'> ");
document.write (" <param name='wmode' value='transparent'> ");
document.write (" <param name='bgcolor' value='#0099CC'> ");
document.write (" <div id='awmflash1' style='position:relative;'><embed id='awmflash1' name='orologio1024' src='orologio1024.swf' loop='false' quality='high' wmode='transparent' bgcolor='#0099CC' width='640' height='480' type='application/x-shockwave-flash' pluginspage='http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash'> ");
document.write (" </embed></div> ");
document.write (" </object> ");
break;

default:
document.write (" <object classid='clsid27CDB6E-AE6D-11cf-96B8-444553540000' codebase='http://active.macromedia.com/flash4/cabs/swflash.cab#version=4,0,0,0' id='centrale' width='640' height='355' align='left'> ");
document.write (" <param name='movie' value='centrale.swf'> ");
document.write (" <param name='loop' value=false> ");
document.write (" <param name='quality' value='high'> ");
document.write (" <param name='wmode' value='transparent'> ");
document.write (" <param name='bgcolor' value='#0099CC'> ");
document.write (" <div id='awmflash1' style='position:relative;'><embed id='awmflash1' name='centrale' src='centrale.swf' loop='false' quality='high' wmode='transparent' bgcolor='#0099CC' width='640' height='355' type='application/x-shockwave-flash' pluginspage='http://www.macromedia.com/shockwave/download/index.cgi?P1_Prod_Version=ShockwaveFlash'> ");
document.write (" </embed></div> ");
document.write (" </object> ");
}


</script>