This game has a lot of bugs on Vista doesn't it? It crashes when you try to polymorph yourself. It crashes when you got too many enemies chasing you (and some baddies really need to be drawn to the nearest village) . It crashes upon saving. But the bug I am pleading for help with is a game ender. Thelyron will not talk --or better said, my character will not talk to Thelyron. He just stands there swinging his sword at the undead necromancer, never hitting, never bothering to parlay.
I've read some guides on this subject and have found that if you cannot talk to Thelyron, you cannot escape the room. If you cannot escape the room, you cannot complete the Mardaneus quest and bring back Mardaneus' sanity. If you cannot do this, how do you get Mardaneus to accept his post on the Council of Seven? If you cannot get him on the Council of Seven, how will they make you the Divine One? If you cannot become the Divine One, how can you win? If you cannot win, your character becomes mighty depressed and then what is the point in playing?
Does anybody know a way around this quest? Better still, does anyone know how to get my character to be able to talk to Thelyron? I am in a bit of a pickle here...

I have not heard of Thelyron freezing before so you may have a new bug. Sounds like the typical freeze. I would walk back to the entrance, if Mardaneus appears, all the enemies will die and a portal will appear, you got a freeze that does not affect the game flow.
If that doesn't happen start hacking away at all the enemies surrounding you, sometimes the frozen will unfreeze for no reason. Kill a few dozen, try talking to Thelyron, kill a few more, walk to the entrance, etc etc. Try freezing Thelyron just for kicks.
You can't use statues, that is a known bug, don't even try. There are lots of posts here in the forum concerning bugs and workarounds. Hope you get him to respond, I know that is frustrating. . . . =)
You did try going back to a save prior to entering the room with Thrlyron and re-entering the room? You have saved and reloaded the frozen Thrlyon game to see if he is approachable on reloading?
You have right-clicked on the game Icon, clicked Properties, Compatibility, check-marked "Run this program as an administrator" ? You have Alt-Tab out of the game to make sure your firewall is not blocking the game from disk writes?
Just asking . . .=)
Edit: you do have the latest video drivers installed?

Well in any case, the patch to 1.005 fixed it. I've only gotten the game to crash ONCE (holding alt in the middle of a treasure trove in the city sewers) after the patch, and I am nearly done with the game. That patch sure is nice.

This is not solved. It happens for me also. Regardless of how far back I load. Shame I was actually getting into the game and now I'm stuck on a stupid bug like this. If no more fixes or updates are released, I'd like a return of my money.

There is a way to fix this bug: Having issues with main quest . Post or email me if you need any help (it is a simple enough procedure if you are comfortable hex editing).

Larian is currently looking into whether the Steam version can be released on GOG, and any outstanding issues.

http://www.gog.com/en/forum/divine_divinity_series/resistance_bug/page4
data.000 ID for Thelyron is Thelyron23, edit the second instance
Thelyron23 Thelyron!¨} hexedit.com

Update: this quest crashing won't derail the main story (the main story will happen just like it would if you didn't do this quest) --assuming you can leave the area, that is.

Once you enter the central room on that level you get locked in and the teleporter stones disabled until Thelyron is dead. Of course with periodic saves you can always reload one before entering and leave that quest unfinished if you don't want to bother with the fix. Completing any of the quests that give an invitation to the castle will result in Mardaneus being cured and (if you have not done the escort quest) the healers moving on their own.

I found a program on steam that fixes this exact problem for me, using the readme and the cmd line, I got it to fix my save file and mark Thelyron as friendly. I'm mainly replying for lost people searching for an answer, since this thread is 12 years old!

Steam thread: https://steamcommunity.com/app/214170/discussions/0/864969953251760289/?ctp=2

Direct Google drive link to the program that fixes hostile NPC issue:
https://drive.google.com/file/d/0BxrVnZpttPneanY0MldZWG51VjA/edit?resourcekey=0-Gta0kHGLQgQYxZ2mCAf5EA