http://www.musesmuse.com
has an active forum with thousands of songwriters, some pro level.
I have heard of dedicated software, but have never used it. I think it makes it easier to do the chord overlays or melodies with the music. Being a whistle player, and not a piano or guitar player, I have no use for it.
As for ideas, many songwriters keep a voice recorder, and/or paper notepad handy at all times. They put down anything that may be interesting, such as an interesting store sign, a snippet of conversation, an interesting stranger, a news story. Many songwriters work from titles. The recorder is extremely useful when a melody line comes. Record it now, or it will likely be lost to the wind forever.
The same secret for prose writers is effective for songwriters, that being spending consistent time at it. For many songwriters the inner editor prevents the flow of ideas. It is good to just let ideas flow onto paper, wordprocessor or recorder, and forget the delete key for a while, then see what a person has that is worth working on. Several of what I consider my best work has come from these throw away ideas.
Two verses and a chorus are plenty for a working song. That’s about 12 lines in the most common format. For a prose writer 12 lines will be five minutes work or they will never finish a book. Admittedly a songwriter tends to have to polish their lines better with rhymes and such, but try just writing without the delete key on some of the topics from the title list. Rhyming software of dictionaries are common tools to help with rhymes. Again, spending consistent time every day on it, will almost certainly produce results.
I’ve met many hobbyist songwriters that only write when they get inspired. For me and others this meant about one song a year, if that. That’s fine for what it is, but think of how well a musician would play their instrument if they only practiced when they felt inspired, and that was only once or twice a year.
What has been most helpful to me, is forcing myself to write at times by participating in a summer Internet challenge, letting the ideas flow freely, and the digital recorder. Hobbyist models are inexpensive now, mine was about $100 three years ago and is fine for field recording.
The summer 50 song challenge has been most helpful to me (July 4 to September 30, each year).
http://www.myspace.com/50songchallenge
Good luck on your journey. Songwriting can be one of the most rewarding of endeavors.