How do I burn files that's larger than a cd using nero???i'm a newbie

You would either need to split the file or get a larger CD.

if it a game...it dont matter...it goes by how long the image is is minutes

i've
burned a game of 780mb

The limitation on burning Data files, games included, to disc is total file size, how can you measure how long a data file is in minutes?, what's the playback speed on a data file then?. :rolleyes:
CDR capacity is quoted as Meg/minutes so a 650/74 will hold 650 meg of data or 74 minutes of audio. To fit more than the quoted capacity on a disc you are overburning it. This writes data to the area of the disc usually used for the lead out track, thus resulting in a shorter lead-out. How much you can overburn depends on your burner and the disc.
Getting 780 meg onto a 700/80 disc is serious overburning, more likely a 90 min (790Meg) or 99min (860meg) disc would be used. Higher capacity discs can be less reliable and not all burners and cd-roms support them.
Also the size of the image file (like those created by Nero,CDRWin etc), should not be taken to be the actual size of the data being burned to the disc. The image file contains overhead that is not burned to the disc and the actual data contained in a 780 meg image file would be considerable less than 780meg.

what's multi-session on nero? isn't that what u use to burn large file than a cd to more than one cd?

nope - multisession doesn't split files, it allows you to burn several files on different writers, or just on different times. hasn't anything to do w/ oversized whatsoever.
try as mentioned above either larger disc's or try to burn the file using overburn, but just max 5, 6 minutes then the disc's capacity. when nero still aborts, then you know you have a really tooo big image.

When you're talking about a 700MB+ file(not an img), try to put in in diff. pieces using eg winzip, winrar, winace...