Miloch,
Per your recommendation from http://forum.baldurs...#Comment_588184 I have DL'd the full fix compilation http://www.shsforums...rri-and-wyvern/ and extracted just the 12 .bam files which pertain to the wyvern crashing problem (mwyvg12-14, mwyvg21-24 & mwyvg31-34) into override. Unless I would experience a similar problem with the tanar'ri, I feel it better to postpone that portion of the extraction.
To remind...I am running just the vanilla 5-CD version of Baldur's Gate with (what I believe is) the most current patch --> 1.1.4315. OS is WinXP SP2. The Vcard is ATI Radeon X300, Driver 8.263.0.0. DirectX version 9.0c.
I just tested it a few times after installing the fix files. The first time, the game crashed as before. The next 3 attempts, however, resolved successfully with the wyvern skulls dropping as designed. I tried it both by leaving a party member outside the cave and with full party entering together. Seems to work in either case. (Please note the attached save file I also furnished in the forum.baldursgate.com thread.)
However, in all attempts, crash or not, the Large Wyverns were not visible on-screen so I was simply attacking the large red circles. The baby wyverns were visible as normal. I can continue to repeat testing of that save to gather a larger sample, but decided to wait to find out if the invisible animations should/can be addressed prior to more testing.
In any case, thank you for your attention and effort to help the community deal with this problem.