how to link togerther some .avi files to create a dvd

[marlo]

How can I do?

thanks/Fabio

[rumplestiltskin]

Install Perian. Convert the AVIs to something QuickTime native (like AIC or a high-bitrate MP4 so you don't lose any quality). Drop the videos into iDVD. If you actually want to connect the videos into one long video, do this using MPEG Streamclip prior to dropping that one, large file into iDVD. Watch out that you don't make the video too long for the disc and quality level you choose in the Project Info window in iDVD.

[Case]

...Or you could not join the AVI files at all, and let the end of part one continue with the beginning of part two by authoring the DVD that way.
If you use Toast, you could select "Play all items continuously".
If you know your way around MyDVDEdit, you could edit the Toast loop by returning to the menu after the last part.