Can I set up Limewire/iTunes so that downloads will go drectly into a playlist ?

Yes, go to LW's preferences; (keyboard shortcut: Command & Comma keys ⌘ ,) and click on iTunes > Sharing & click option at top for Share My Music. Put a name you can identify in the Shared Name box if there isn't one already.

This will show a LW Playlist in iTunes. However, don't be fooled, this means iTUnes is referencing the songs from your LW download folder and the files are not in your iTunes music library. So if you remove the songs from Download folder, they will not be playable in that playlist.