Starkeeper, if you don't need a harmonizer then you can very economically build a software based arranger:
Live-Styler for Auto Accompaniment $30
LiveSynthPro & DXi Host/Wrapper $100
sYnerGiGs Wavetable $20
Soundfonts mostly free
So for around $150 (assuming you already have a computer and controller keyboard) you can have sound equivalent to the top end arranger keyboards. Amazing!!!
Now if you have an Audigy 1 or 2 Soundcard you don't need LiveSynth Pro. You just load the sYnerGiGS wavetable into your Audigy Soundcard and use Live - Styler and start playing. This would save a few bucks. In addition you could use the effects of the soundcard, e.g., reverbs, chorus, delays, etc.
If you want to take the next step then Kontakt would be a good choice (expensive). Kontakt can be operated as a standalone softsynth but you usually cannot have more than one application running on the same audio drivers. There is a way around this by operating LiveSynth on WDM and Kontakt on ASIO drivers for your soundcard.
Similarly, the B4 can be used as a standalone or DXi or VSTi. So if you were going to go the route of Kontakt, B4 and LiveSynth then the best approach would be to use a DXi Wrapper/Host, e.g., Brainspawn, Project5 (expensive) or Sonar (expensive), etc.
LiveSynth will play any soundfont wavetable. sYnerGiGS comes the closest to XG. If you have the energy you could build your own full XG Wavetable. I find sYnerGiGs sounds very good on most Yamaha styles and midis. I have made alternate wavetables using sYnerGiGS as my base and improved the pianos, strings, brass, bass, etc. The wavetable I now use for my accompaniment is up around 128 mb.
[This message has been edited by Frank L. Rosenthal (edited 08-29-2003).]