Regarding jittery sound, slow gameplay, mounting, etc:
If you feel a game is running too slowly or the sound is jittery, then firstly you need to read the documentation. It clearly explains that you have to play around with the frameskip and cpu cycles to get things running smoothly. Each game will require diff. params to run correctly because every game taxes the virtual CPU differently.
Regarding mounting of the DVDROM drive: Default mounting is fine. If there is no disc in your drive, then it probably will not mount. If the media you are trying to mount is not xbox-compatible (e.g. not burned via XISO or in UDF format, etc), it won't work.
If you want to mount the F drive, then type this in at the command prompt:
mount f f:\
Where the first "f" is the DOS drive you want to map to and the "f:\" is the XBox drive.
The XBox drives you have available at startup are:
C, D, E, F, R, X, Y, Z
D is the drive/dir in which dosxbox.xbe is located. R is the DVDROM drive. All the others are the standard drives.