I have now tried what MCE2KS suggested. Unfortunately, it makes my computer freeze half way through (when it initially loads up it says that I don't have sufficient memory for it to work - it says something about needing "20gb" but "can only find 4").
I use "MediaCoder" to convert AVI into MPEG1 files. Then either "CombiMovie" or "MediaJoin" to join the MPEG files together and then "SoThink Movie DVD Maker" to convert to a DVD. All FREE and all can be googled for. Try them.
"VLC Media player" and "VirtualDub" are also good FREE program to have.
I really don't know what i'm doing! I have now managed to convert an AVI into an MPEG but am totally confused now and feel like I am back to square one - as I still don't seem to have any software that will put the MPEG file onto a dvd disk.