Hi there again,

is it possible to highlight a certain marker?

You mean like this? http://www.openstreetmap.org/?node=539718625

You can also replace the “lat”, “lon” within the permalink by “mlat”, “mlon” to show a marker.

Is it possible to have more than one marker? Say I have to show 10 locations?

If you want more markers, you are probably best using OpenLayers. Something like this example: http://wiki.openstreetmap.org/wiki/OpenLayers_Marker_Example
Or with the POI markers in a separate file, like this: http://wiki.openstreetmap.org/wiki/Openlayers_POI_layer_example

Or you could try this page, which is an easy way generate all of the code for a map with markers where you choose: http://osmtools.de/easymap/