Thanks for the hint. I managed to solve the problem. If anyone wants to try it, here is the code:
<div class="serendipity_entry_body">
{$entry.body}
{if $entry.properties.ep_googlemapvals and $entry.properties.ep_googlemappoints and $entry.properties.ep_googlemapwidth and $entry.properties.ep ...

The following s9y-code
function load() {ldelim}
if (GBrowserIsCompatible()) {ldelim}
var valstring = "{$entry.properties.ep_googlemapvals}";
var vals = valstring.split(",");
var map = new GMap2(document.getElementById("map{$entry.id}"));
alert('map.setCenter(new GLatLng('+vals[0]+', '+vals[1 ...

I already did this, even with the whole command and it looked exactly like it should do. Any other idea, what happens?

Hi, I tried to make the whole map thing a bit more configurable. So it looks like this:
<div class="serendipity_entry_body">
{$entry.body}
{if $entry.properties.ep_googlemapvals and $entry.properties.ep_googlemappoints and $entry.properties.ep_googlemapwidth and $entry.properties.ep ...