Instructing is a good way to build hours and you will be logging PIC whenever airborne with a student. Remember however that JAR now require 500 hours multicrew time before they will unfreeze the ATPL. This requirement however will usually be fulfilled when you are in your first airline type employment in the right hand seat. The only bearing being that you options will be a little limited until the ATPL is gained. In many environments however it will have little impact as you would find bonds etc with the airline would take you well beyond 500 hours multicrew period. Plus the fact if your moving on to something substantially bigger you will need the 500 hours to become profficient.