ALSA configuration

[a monkey]

In XMMS' ALSA configuration, there are values called `Buffer time' and 
`Period time'. I have no idea what those are. If I play around with 
these values, I can get my music to sound a lot nicer. But how do I know 
what the best values for them are? Also, there is a checkbox called 
`Mmap mode'. Should I have that checked?

By the way, if this info helps, I am on an eMac G4, 700 mhz processor.