I have completed the Echelon version (w00t). I too have GeForce FX 5200. Other specs: Pentium 4 2.0GHz, 768MB DDR-RAM @ 266MHz, WinXP Prof. SP2. Crashes can happen if:
-> You press buttons quickly (for instance you press the Cancel button to exit a menu before it has even loaded completely [but in the real Dreamcast it would just put your command in a buffer so as to execute later]). Even though it doesn't crash at once, you first experience a sound problem (many sounds and BGMs sound really bad, can't describe but you've probably experienced)
-> You play too long (a bit obvious, but I thought I should mention). Note, however, that I managed to play 5 consecutive hours (I did save at regular intervals of about 5 to 20 minutes though) before I closed Chankast not because it crashed but because I got bored. The sound did go off at times but would fix alone a bit later.
When in an airship the emulator is more prone to crashing than otherwise. Also, to avoid pressing buttons too quickly (first point), try setting the Chankast clock (with the +, - buttons) to such speeds so that the game NEVER exceeds 25FPS. I played it at about 15-20FPS to ensure that. Of course that means that the game pretty much plays in slow motion, which explains why I needed 50 hours for my 20 hour game. If you want any game saves I will post my memory cards sometime in late May. Oh, and I've been through the game TWICE!!!
Does anyone else feel too that the game should have more side-quests?