Jvc evario- giga dvd burner on P4 pc- problems in dvd burning

i bought a jvc evario 20 gb hard disc dv camcoder and recoded some class sessions- discussions.
after transfering about 30 sessions on to an iomega external hard disc, using power plus gold 2 softwr i tried to copy 4 sessions in one dvd r…and everything went on well for a few copies…as a matter of fact once i opted for 4 copies of same, the remaining 3 were super fast.
however my happiness was short lived and after abt 20 dvds, i am having problems. after one hr or one and half hr i get message that dvd writing failed…some times the cd becomes useless and most important thing as a volunteer, i had promised to do this free for this group and now i am failing very badly…

kindly note that i am not a professional and i know only to do exactly what u tell me to do…meaning open …click etc once specified, then i can do that only…

kindly help me to solve this

thanks a lot in advance