Kay, what are you trying to make an ISO of - a Video DVD or a PS2/Xbox DVD (game)? There's a bounty of guides on making Video DVD ISOs on the Net, some still here at aD. Even more over at VideoHelp. Easiest route to make a Video DVD is DVDDecrypter in ISO mode. Rip the disc in ISO mode via Decrypter, burn ISO with Decrypter. as for burning an ISO with Nero, goto Recorder - Burn Image and browse your HDD/Desktop etc till you find the ISO you are looking for, select it click OKAY. Insert blank DVD, click on Okay and Nero oughta do the rest on its own
No problem. Just nexttime, try to be more specific what kinda media (VideoDVD or PS2/Xbox) you are using as a source since the process is diferrent for each.