I know you have probably bought Nero 7 and want to use it, but for ISO's I would recommend Imgburn. It is free and is purpose built for burning these types of files.
Where did this ISO come from? DVD rip or download? If a rip, then rerip making sure that your rippers are up to date. If downloaded, you may have a bad file. If a rip what is the name of the movie?
When you say you have an ISO, i assume you've mounted it on a logical drive? If so, and you have access to Nero, then mount the iso, and use the "back up dvd" feature in nero to duplicate the mounted disk to a real one.
ImgBurn and Nero both do a good job of burning ISO images. I do it all the time. Since the question was on Nero, I'll post a capture showing the quick "how to". If the files in the ISO are DVD compliant they play on a standalone player. Mine do all the time. Just open Nero Express from StartSmart and follow the indicated path. http://img178.imageshack.us/img178/7920/neroexpressisoburntz7.png (picture changed to link by creaky as it was throwing the page margins out) As you can see, I've been working on my video library and did a lot of backups to ISO for burning.
If it's a download, is it in DVD format or AVI? If in AVI, Nero Vision may need to be used for conversion. Since you have Nero you can open the ImageDrive in the Tools section of StartSmart. You can use that to open the image the same as putting a DVD in a drive. What you have is a virtual drive and the ISO is a virtual DVD. You can check the files to see if they're in the right format, Video_TS with the IFO, BUP, and VOB files. You can also play the files from ImageDrive in the Showtime player, if they're in the right format.
have tried that packman but all it does is copy image to dvd, i still cannot play the film in my dvd player, am i missing something
Where did you obtain this ISO from? It sounds like it isn't in a DVD Compliant format so you should try the following. 1) Use DVDShrink and open up the ISO by going to file and selecting open Image. 2) Then just let Shrink back the movie up as an ISO 3) now you can burn the image produced by Shrink with any burning software (I recommend ImgBurn)
If the ISO image is burning and doesn't play, that indicates it's not in a DVD compliant state, whether the files are MPEG2 or not. That's why I suggested taking a look at the contents of the ISO. The question is what is in your ISO? First off when you open the Image, there should be a folder named VIDEO_TS and maybe one named AUDIO_TS (empty). When you open the VIDEO_TS folder what is there? There should be a group of files with IFO, BUP, and VOB extensions. Some have more than others. There shouldn't be anything else. Is the content right as far as the file types? I suggested opening the ISO in ImageDrive to see if it would play. Did you use ImageDrive to play the ISO in Showtime? From what has been said so far, it sounds like the files aren't DVD compliant and may not be in DVD format. Answer the questions and we'll have a better idea of what you have.