Someone else is having the same problem in this thread.
PinkFloyd2003 seems to have solved it for at least himself. http://www.gog.com/en/forum/myst_series/crashing_issue/perm=6/#p_b_6
Maybe you could try his sugestions and hopefully it works for you. Well at least the ones that will apply to you as your already on xp, like 640x480 and 256 colours.
Tkx for the info but i've tried all the configs still no intro, puzzle not working and still crashing at the clock tower! Here's my dxdiag info :
Operating System: Windows XP Home Edition (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_gdr.090804-1435)
Language: English (Regional Setting: French)
System Manufacturer: GBT___
System Model: AWRDACPI
BIOS: Award Modular BIOS v6.00PG
Processor: Intel(R) Pentium(R) 4 CPU 2.50GHz
Memory: 1016MB RAM
Page File: 388MB used, 869MB available
Windows Dir: C:\WINDOWS
DirectX Version: DirectX 9.0c (4.09.0000.0904)
DX Setup Parameters: Not found
DxDiag Version: 5.03.2600.5512 32bit Unicode
Riven works perfectly... I don't know what i'm doing wrong with Myst!
Will send to Gog's support team as well to see what response they give me.