Hi Boslandew, bfisk explained RNAV pretty well another point to learn more about it is
EUROCONTROL Navigation Domain - Home the eurocontrol domain about RNAV and RNAV applications.
About your question to the 737, a lot depends on variant, weight (load factor, fuel) and to some extent on SOPs. Usually a take off is done with reduced thrust and pretty every time with reduced climb thrust as well. After the third segment typical climb rates are between 2500 and 4500ft initially, however those will reduce as you climb, if heavy sometimes doing the last few flightlevels will be very slow indeed. Descends are usually done with idle thrust and initial descend rates can be quite high. Speeds for climb and descend depend on cost index, in todays economic climate it is often quite low and the speeds slow.
A good place to learn more about the 737 is smartcockpit (google it) and
The Boeing 737 Technical Site.