Usually to convert Real Media files to MPEG you may use the following software:

1. Video converter to convert Real Media files to MPEG

2. DVD burning software that can burn Real Media files to DVD directly.

In your case it really depends on what kind of .smi files you have.
Usually .smi files are simple text files describing audio/video stream and subtitles sources. You may try to open them with a text editor to make sure this is your case.

If your .smi files have links to Real Video files only, then you're lucky 'coz you can simply use the 2 ways described above.

If they also link to subtitles that you wanna see on a DVD, then you should use screen capture software to capture from the Real Player.

I've also seen .smi files that were actually .rm files with wrong extension. Such files can be safely renamed to .rm files for the latter video conversion. And they can be easily ditinguished from .smi text files by the file size. Text files are usually of a size less than 1 kb.