Normally you prefer ALSA and if it works for you, then fine. If for some reason alsa can´t be made to work or generates unsolvable errors(actually very rare cases, I think) then you try OSS.
ALSA supports many older chips, like ISA ones, so nobody should have problems with this.
alsaconf doesn´t build a kernel module, it only detects installed sound cards and configures ALSA to use the proper driver, if available(the driver already exists somewhere).
ALSA and OSS comunicate with the hardware and provide an abstraction for other higher level programs like the esound daemon. Esound provides more advanced features, while OSS and ALSA provide the low level stuff. In addition, ALSA provides an emulation of OSS if some old programs need it.
I´m not a specialist, but I hope this makes the things a bit more clear for you.