Thought I'd share my experience in case it helps anyone who is new to this.

I'm an amateur musician who's used Linux for everyday computing for about 10 years, and recently decided to use my laptop as a tool for composition.  I'm no hacker but reasonably competent at configuring Linux apps.

I use a Toshiba 64-bit laptop running Ubuntu 9.04 (2.6.28-3-rt kernel).  Sound and video hardware in this machine is the usual Intel OEM stuff - nothing special.

I decided to try out a number of music applications but had a lot of problems installing/configuring the likes of Rosegarden, MuseScore, and a few others, and setting up the jack server, minimising latency etc.  I tried all the solutions posted in relevant lists and forums but still found problems and eventually got fed up - I'd rather spend the time writing music. 

Then I found NtEd.  I'm surprised there is little mention of it in the archives here.  I found it to be the only serious composition tool that installed and ran without any problems, and very easy to use.  If you want to make use of midi, the latest version ( 1.8.0 ) supports creating a score from playing a midi keyboard.  The developer's website and documentation is comprehensive and well written.  So if you are more interested in composing music than tweaking Linux music apps, I recommend you check out NtEd.

Michael