I you can read danish (I see you are from Denmark), there is a danish manual to your machine available here:http://www.quahwa.dk/product.asp?product=39
It sounds weird that you get no crema, are you using freshroasted coffee? How much coffee? and how long does it take?
I also have a Vibiemme Domobar (single boiler like the one you got) and my best advice to you is to get a naked portafilter and a triple basket and make a lot of experiments (the forementioned Quahwa sells both items cheaply). I have found that I get best results with a triple basket and 16-18g coffee. Also, read most of the topics mentioned here: /faqs-and-favorites-digest.html
EDIT: I forgot one thing: I could not pull good shots when I first got my Domobar, as the OPV was set to allow too much pressure -- what does the gauge show when you make espresso? I would recommend you adjust it, if the pressure is higher than 10 bar -- I adjusted mine to around 10 bar.