There are three methods:
1) Convert from srt to sup format and author using IFOEdit.
2) Convert to SSA format, and use MaestroSBT to convert to SUB format, which can be used by submux-dvd from linux ported dvdauthor package
3) Convert ot spruce up format (using Subtitle WorkShop) and import in DVDMaestro.
If you want menus:
linux ported dvdauthor allows you to create menus using a XML file, but you might find easy to do method 1 or two and then import the VOBs in DVDLab to create menus. But in this case you'll have to fix the IFO information, following this guide:
http://www.dvdrhelp.com/forum/viewtopic.php?t=179271
DVDMaestro nativelly supports subs and menus, but it's no longer produced...
, i bough a japanese dvd of saint seiya hades saga , it has no subs and what i would like to do is add subtitles to the vobs and make a back up with subs, i would like them to be on/off, what should i do? *i have the subs in .srt and .ssa, the dvd is dvd5 so no need to recompress* plz help me 
