Hi,
This is a little late but hopefully it'll still be of some help.
Your episode-num element should look like this:
<episode-num system="xmltv_ns">s.e.p/t</episode-num>
Where s is the season number minus 1.
Where e is the episode number minus 1.
Where p is the part number minus 1.
Where t to the total parts (do not subtract 1)
so Season 7, Episode 5, Part 1 of 2 would appear as:
<episode-num system="xmltv_ns">6.4.0/2</episode-num>
Any section can be left blank (at least according to the xmltv spec). So your example would appear as (assuming you were referring to episode 10):
<episode-num system="xmltv_ns">.9.</episode-num>
Do a google search for "xmltv dtd" to see the full spec.
Good luck
Adrian