Yep this works.

1) Install the Lastfm app
2) Install Vagalume (I use this to control the lastfm library)
3) Go to the N900 Settings (The main Phone settings icon)
4) Scroll down to the bottom and you'll see the Lastfm Settings.
5) Enter your lastfm username and password
6) Open Vagalume and go to the settings on the top
7) Select, Play Radio - My Radios - My Library

And Bingo. That should start playing your lasfm library.