Head gasket

I'm not a mechanic.How hard is it to replace the head gasket?What should I look out for?Anything I should do while the head is off? How long should it take?how do I make sure the head is good?Valves?Where should I get parts for it is there aftermarket?It is a small combustion gas leak into the glycol so far how do I make sure the motor deck (where the head sits) is OK?Sorry for all the ?s but both our vehicles are down with this problem and we can't afford to have a shop repair them @ $1100-1300 each.please email me at snipped-for-privacy@webtv.net