|echo ^G at the command line (echo Control G) will allow you to hear the famous 'beep' to test your pc speaker.|
As far as a Dos Driver, what program(s) or game(s) are you trying to use the PC speaker in? USUALLY, the software doesnt need a driver, if it does it will be unique and individual for the program, in order to use the PC speaker (its usualyl an option in settings on older dos software). I see alot of people above are reccommending using the windows PC driver, i dont see why, being that you specifically said 'PURE MS DOS mode'. But like i said, there really isnt any PC Speaker driver for dos like there is for windows. This is because windows programs all run off the same system drivers which are built into the registry, dos doesnt have a registry, and all dos programs use thier own operating environements, guis and drivers. Tell me the software and ill see if i can help you get it working.
Also, what is the sound card you have installed, do you know? Try and be specific if possible.
Hope this helps, let me know if i can be of more assistance.