Okay, here's how you can do it.
Go to your admin CP. Go to custom BB codes, and to add new BB code.
Now, add the following stuff:
Name: Last FM (doesn't really matter what you call it)
BB code tag name: fm (so the code will become [fm]name[/fm])
Replacement:<img src="http://games.onego.ru/lastfm/black/{param}.png"> (this is the code needed to show up.)
Example: [fm]DJHenriette[/fm]
Description: Show your latest Last FM songs.
Use option: No.
Hope this will help you.

I tested the code and it sh?uld work.