Loneliness is marked by a sense of isolation. Solitude, on the other hand, is a state of being alone without being lonely and can lead to self-awareness

--------------------------------------------------
Note added at 6 mins (2008-02-17 16:21:59 GMT)
--------------------------------------------------

Loneliness is a negative state, marked by a sense of isolation. One feels that something is missing. It is possible to be with people and still feel lonely—perhaps the most bitter form of loneliness.

Solitude is the state of being alone without being lonely. It is a positive and constructive state of engagement with oneself. Solitude is desirable, a state of being alone where you provide yourself wonderful and sufficient company.

Solitude is a time that can be used for reflection, inner searching or growth or enjoyment of some kind. Deep reading requires solitude, so does experiencing the beauty of nature. Thinking and creativity usually do too.

Solitude suggests peacefulness stemming from a state of inner richness


--------------------------------------------------
Note added at 12 mins (2008-02-17 16:27:22 GMT)
--------------------------------------------------

As per-http://www.free-tarot-reading.net/articles/ali_hermit.php-
the difference is solitude is something you WANT and feel comfortable with, a peaceful, relaxing and inspirational space, and loneliness is an UNWANTED experience of being on your own.