Carillon are the alienware of audio pcs… http://www.carillondirect.co.uk
also, if you go with dell, watch if you use any digidesign/pro tools stuff as they are pretty sticky with support for any models outside a set few, but you can find info on this on the digidesign website
I use a Sony Vaio for audio production and some location recordings and its been good to me – after you get rid of the gumpf they install on the thing.
I have regretted not getting centrino though.
few things important to audio pc fast processor, LOADS of RAM especially if your gonna be working with VSTi/DXis etc, and if you are recording straight to internal HDD then make sure its a fast one.