You get one title for all input mpegs with a chapter marking at the beginning of every file.
If you want to have multiple titles on your DVD, you have to separate the titles with the '-t' option. Each '-t' marks a new title and the following mpeg files will be authored into this titleset until a new '-t' appears. So, to author two titles onto a DVD, issue
#> dvdwizard -t mytitle1.mpg -t mytitle2.mpg
The resulting DVD will show two titles on the VMGM menu, the first called "mytitle1" and the second "mytitle2".
The '-t' option may be followed by a filename or a string, which then will be used as the title for the movie. E.g.
#> dvdwizard -t "My first movie" mytitle1.mpg -t "Another Movie" mytitle2.mpg
will basically produce the same content as in the first example but the VMGM menu will show "My first movie" for the first title and "Another Movie" for the second one.