Hi,
Well, first of all just try running a cable from your Rotel preamp (which I'm sure is absolutely fine) to the input jack of your laptop. Many modern laptops do now record in stereo and a quick test will reveal the truth. The cable you need is readily available and is pictured here:
http://www.alpinesoft.co.uk/VinylStudio/connecting_up.aspxIf you find you are recording in mono, the Griffin iMic is a nice little device but it doesn't work with Windows Vista. Behringer also make a couple of suitable devices for around the £30 mark, e.g.
http://www.chemical-records.co.uk/sc/servlet/Info?Track=UCA222HTH