I am using a Zoom H2 (line out connection) connected to the laptop (line in connection). When using audiorecorder in my script the sampling rate is 8 KHz. I really think it is a Matlab/Windows 7 related problem because my audio sound/record features all work perfectly when I play mp3 files and when I use the record feature out of the Windows accessories. Also when I listen to streaming sound from some of the webcams (Smalls Live Jazz, for example) the sound is quite good.
And, as I have said (I think), the audiorecord and soundsc functions work fine on my XP laptop.