FL Studio is the most complete virtual studio currently available. It will play any sample file (wav), generator (softsynth), VSTi & DXi) or midi instrument you feed it.
You will be creating wav, mp3 or midi songs or loops only minutes after launching it.
Minimum System Requirements
Pentium III or Athlon XP (any processor supporting SSE instructions)(or) Intel Mac with Bootcamp (running XP or Vista)
Windows 2000/XP/2003/Vista (32 & 64 bit)
256MB ram
200MB free harddisk space
Windows-compatible soundcard with DirectSound drivers. ASIO drivers are required for audio recording (FL installer comes with generic Asio4All drivers)
It's really great for loop (it's name is loops) I use it to jam 'n' record
Enjoy!