What is the difference between the glycolate pathway and photorespiration?
The simple answer to the question posed in the title of the question is as follows. The glycolate pathway is the series of reactions converting phosphogycolate to reusable carbon intermediates + CO2. Photorespiration is the combination of two processes:


The oxidation of the enodiolate intermediate on Rubisco to phosphoglycoate + 3-phosphoglycerate.
The processing of the phosphoglycolate produced by the glycolate pathway.


You cannot use the two interchangeably as there is no respiration (use of oxygen) in the glycolate pathway. The glycolate pathway is just the latter part of photorespiration. I'm not sure what the text books are that confuse the two, but Stryer presents this quite clearly in Figure 20.6 and 20.7 at http://www.ncbi.nlm.nih.gov/books/NBK22344/#A2795.

I am not familiar with the term "conservation pathway" in your final question. I would call the glycolate pathway a "salvage pathway" (although this term is more commonly used for recycling the skeletons of the products of macromolecular, esp. DNA, degradation). It does not salvage all of the carbon skeleton of phosphoglycolate as some carbon is lost to the atmosphere as CO2.