Two questions:

First, what would be the most suitable method for interpolation where the data is:

1. Mostly increasing with an exponential/ logarithmic trend.
2. Has several abrupt drops in y.

Should I try some means of interpolation where I split the data into several sections (to avoid the drops) or is there some method that would take them into account?

I have access to Openoffice and (with some effort) Excel. Neither provides a obvious solution.

Second, does anyone know of a decent text on the subject of statistics (and regression, etc.) that is not too deep, but good enough so that I would have an idea where to begin if faced with a statistics problem?

I would be most grateful for whatever insight/ advice you could offer.