i ghanged my head gasket about two weeks ago and it was no problem though a valve had snapped while the car was parked up overnight sumhow lol
http://www.youtube.com/watch?v=EdeYBPC3YeM
if you watch this video on youtube of sum boyo changing his head gasket your not going to be far wrong. although tightening head bolts is 20nm then angle tighten a further 120 degrees. if the only thing you change is the gasket and dont get the head skimmed or anything it will cost a tenner for the gasket.
oh and timing holes. a tiny one beside the oil filter and one in the cam shaft. do do this correctly take the timing belt cover off and hand rotate it til the hole in the pulley lines up with a hole in the head. the postion is roughly 2 oclock. then the bottom 6mm drill bit should slot ryt in. to double check that it is in fully take the bolt or drill bit out of the cam pulley hand gently hand turn again and u will see the drill bit move about and you will be prevented from moving the pulley that far. the dude in the video shows this aswel.
a garage would charge 300-400.