I followed these easy steps to get Last.fm working on my N900 via Vagalume:
1. Goto Last.fm to request an API Account http://last.fm/api and take note of your API Key and API Secret Key.
2. Download the LastFM.zip file from nokiAAddict downloads HERE
3. Unzip the LastFM.zip
4. Edit the LastFM.xml and replace the ADDKEYHERE and ADDSECRETKEYHERE with your API Key and API Secret Key.
5. Transfer the edited LastFM.xml file to your N900.
6. Open Vagalume and select Last.fm/Import servers file… and browse to the LastFM.xml file you just transfered.
7. In Vagalume select Last.fm/Preferences and set Service to LastFM.
NOTE: You may need to restart Vagalume?
Enjoy Last.fm on your N900 using Vagalume 🙂