1 Gross pay should be shown along with your UK P60 up to March 2008
2 Exchange rate is approx .684 but Revenue will apply the exact rate anyway.
As the two year ends do not coincide, Revenue will take 74% (i.e. 9 months out of 12) of your UK income in the year to March 2008 and apply it back to ROI 2007 year to 31st December 2007.
This will be added to your gross ROI income for 2007 (include your p60) and taxed in the normal way at 20% and 41%
You can claim the full Paye allowance and Personal credit which will reduce your tax bill.
Divide your net tax by the total € income to give a transborder % rate say 10%
Apply the 10%say to the € equivalent of your gross uk income to give Transborder Relief. You can reduce your final tax bill by the transborder relief to give any additional amount due.
It is complicated to say the least
At the end of the day you should not have to pay any further PRSI on this - and only a small amount of PAYE depending on the split of € earning against UK earnings.