I'm not familiar with Acid Music Studio nor Riffworks, but I know many Line 6 users also use Riffworks - it has line 6 Edition I believe, and a trial period.
There are many, many recording programs. If you're just starting you might want to try something simple (and free!) like Audacity. There are also inexpensive products like Cakewalk's Music Creator. There's also Ableton Live whicvh I know many Line 6 users recommend.
There's also a discussion forum here in the Line area that focuses on Home Recording. You miught get some tips here:
http://line6.com/community/community/support/computer_based
Hope this helps.
