Use of DIG, DCD, NCD

Hi, I am a VB and C# programmer and now getting 'into' PBP. I have 3 questions:

1) On reading through the manual, I see DIG, DCD, and NCD operators. I'm sure the designers had some cunning ideas in mind when they created them, can anyone give me some examples where/why they might be useful to me?

2) What is the difference between the DATA and EEPRom statements?

3) Does anyone have a link to a table/app note linkinh SOUND to actual musical notes or frequencies? - why not just use FREQOUT?