I'm using the original Last.fm Scrobbler, it works great with winamp.
The only thing I don't like is that it won't terminate when Winamp is closed...
for this issue I've created a plugin that terminates the scrobbler process
(the process name is editable in a config file)
if anyone is intereseted:
last.fm Scrobbler:
http://www.lastfm.de/download/windows
last.fm shutdown winamp plugin:
http://www.rimkus.it/www_rimkus/down...20Auto%20Close
Kind regards
Raver