Yes, that's what I'd try.
Load the AVI into Virtualdub and cut into two separate AVI and then use
ConvertX to make two 2-hour DVD's.
about dvdShrink
http://en.wikipedia.org/wiki/DVD_Shrink
http://www.dvdshrink.org/forum/viewtopic.php?f=1&t=10056
how to use dvdShrink
http://www.doom9.org/index.html?/mpg/dvdshrink31-main.htm
where to download it
http://www.afterdawn.com/software/video_software/dvd_rippers/dvd_shrink.cfm