VRO files came from a home video recorder most probably - this are the files when the recording format is DVD-VR (probably the same if +VR - I've a Sony and only used it with -VR and using a DVD-RW).
I guess what taktik intends to do is to produce a regular DVD video using VRO files as source, not exactly a conversion of files as VOB result from the authoring process of a DVD and if the disc from the home recorder is finalized most players can read it with no modification.
If the idea is to edit the files, I guess the best is to import them to a video editor that turns the VROs (during the import process) to Mpeg2 DVD compatible files, and after the editing to author a DVD.
I've done it with Ulead's VideoStudio and it works.
I understand some authoring packages can also take VROs directly, if the idea is to mix them (with no changes) with other files to produce a DVD.
I don't know how to split them, but the packages indicated by coathi may work for one or both these ways.