some additional general remarks to the above:
i've encountered several different cases (and there might be more!), which i find quite interesting. it means that the audio database of MZMP is not 100% coherent or structurally uniform but any posted album can have different 'properties'. Apart from the fact that the streaming url can
always be read from the
Temporary Internet Files folder, we have:
case a:
album has some 'Album Only' tracks and they cannot be previewed at all and you can guess their streaming url and download those tracks in full-length with the default method. (the Michael Jackson This Is It)
case b:
album has some 'Album Only' tracks and they can be previewed in full-length and their streaming url's download full-length *.wma's.
case c:
album has some 'Album Only' tracks and they can be previewed 30secs only and their streaming url's download 30secs *.wma's. the other tracks play (and 192k-download) in full-length but their streaming url's download, again, only 30secs *.wma's.
case d:
album has exclusively 'Album Only' tracks and they can be previewed 30secs only and their streaming url's download 30secs *.wma's.
case e:
etc.
etc.
Other cases might be possible -- so it is a matter of luck if your mms/rtsp url downloads a full-length *.wma; it depends on the album (as provided by the publisher/label) and maybe even Microsoft might be responsible for this. To sum up,
30secs previews most likely mean you're busted!
EDIT:
read on, you are not busted! 
. some clever boardie found a way to convert the 30secs url's to full-length url's. Congratulations to this key discovery!!! great 'team work', hehe...