I am a newbie with subtitling.

I had some 8mm movie reels that I had converted to a DVD. I would now like to go back to that DVD and add subtitles to the video. The sound is just a background music soundtrack that was added during the initial conversion because 8mm movies did have sound. The soundtrack can be deleted.
I am using Subtitle Workshop v2.51, Windows XP, and I have installed the Full Coda Codec Pack.
When I open the .VOB files and play it in the preview, the time index runs till about 12 seconds and then it stops. The video runs for a little while longer, and then it locks up.

I can play the video without any problems on the PC outside of the Subtitle Workshop.

Can anyone please help me with this?

Thanks