Well there's 3 different types of tax, PAYE, PRSI, & USC, and they all have different thresholds
For a normal single guy with basic tax cut-offs & credits etc the weekly thresholds are
PAYE - €317.31
PRSI - €352.00
USC - €193.00
so he can earn €193 per week without paying any taxes whatsoever but even if he earned €317.31 he would only pay about €9.11 in USC and that would be it as far as taxes payable goes.
Those figures are based on a full year, he would have some unused USC & PAYE cut-offs so realistically if he has no other income in 2012 he could earn a lot more than €193 week between now and the end of the year and pay little or no tax at all.
Hope that helps