Is it an inheritance ( father deceased ) or a gift ( father alive ) ?
If inheritance then you can get €521,208 ( 2008 amounts) from parents before Capital Acquisitions Tax becomes payable.
If gift, then the same threshold above applies for the child but the parent could face Capital Gains Tax on the disposal unless the disposal can come within the remit of "Disposal of site to child" ( Section 603A Taxes Consolidation Act 1997) whereby a parent can give a site not exceeding €500,000 in value ( €254,000 up to 2007 ) for the purposes of the child building their principal private residence. If qualifying then no CGT falls on the parent. However there are strict rules on both size of site and the child actually building a PPR on it.
The CAT thresholds and PPR reliefs quoted are for parent to child. Your girlfriend is a stranger to your father and her CAT threshold would be only €26,060 (2008 amounts).
You should discuss the implications of all this with your legal advisor.