"Are there any other programs that can allow divx avi files to play on much older dvd players?"
it dont matter if it's old or not... cause if a DVD Player dont support DivX/XviD then you need standard DVD format assuming a VCD/SVCD aint a option.... but my APEX DVD Players support SVCD which i used to use often until DVD Burners and Discs got cheaper (now SVCD's are just more costly to burn to CD's since 2-3 CD's cost more than 1 DVD+R disc nowadays and you get alot more space on DVD to) and now i just use XviD format since my XBox1 running XBMC can play them well.
but typically speaking i usually just use "Gordian Knot" to convert DVD to XviD format.... no one really uses DivX anymore since XviD is pretty much 'the standard' (not to mention FREE) for .avi stuff.
p.s. in general im not a big fan of converting .avi back to dvd format since it just lowers quality... if you want a standard DVD just copy the original DVD.... but in general if you got alot of .avi (XviD/DivX) files i highly recommend getting a original XBox console and softmoding it so it can run XBMC (XBox Media Center) this way you can play the .avi files directly with no conversion.