If you just want to change the LW downloads to iTunes
You could use this conversion program
iTune Associator 1.6 (freeware) 40k download
available from........

http://homepage.mac.com/josiahpugh/itunesassociator/
or from versiontracker.com
(OSX is not supported by iTune Associator 1.6)

I've used Associator 1.6 to convert QuickTime and other mp3 audio files to iTunes,
works fine for me;
Converts individual files or all (non-iTune) items in a folder...
just dump them (or it) onto the Associator icon and they are now all iTune items
and a double click will launch iTunes and play them.

Recently though, I have set up LimeWire to "share" the iTunes Music folder
which already had all of my mp3's in it.
HD>documents>iTunes Music
Now, all of my new LW mp3 downloads go there
and become iTune documents (w/o using Associator).
They then get added to my iTunes Library when I click on them for the first launch.

LW also sends my "incomplete downloads" to a
iTunes Music folder>incompletes
as iTune files which I can check to see (hear) if they are OK for a future (complete) download.
And, unless I move a "incomplete" to the iTunes Music folder (I DON'T),
the incompletes show up in my iTunes player
but are NOT listed as "shared" files in LW.

AND WE DO NOT SHARE INCOMPLETES, DO WE!!!!!!!!!!!!!!!!!!!!!!!!!!!!!