The answer to all your questions is in the Datasheet for that PIC - make friends with it - and in the PBP manual...

You access the registers exactly the same way as you would in C. The Register names are used directly in PICBasic (see PBP manual section 4.10).

For example... (answering your Q1)...

The value of Timer0 is contained in Register TMR0. To read this register say into a variable you simply do...

MyVar=TMR0

to preset a value into Timer0 (answering your Q2), you do the opposite...

TMR0=MyVar

or (to preset a value say $F0)

TMR0=$F0

All the information you need on the prescaler (answering your Q3 and Q4) is in Datasheet section 2.3.2 - OPTION REGISTER.

Melanie