all the characters blink rapidly and have spikey graphical artifacts shooting out of them, and after a while the game just crashes and results in a BSOD... any idea? btw, running on vista

Could you please provide a little more information on the system you are running the game on? What sort of video card and cpu are you using? What version of vista is it 32bit or 64 bit?
I would also advise contacting gog support with your issue and send them a dxdiag.
For now all I can recommend is you mess about with compatibility settings and allow the game to run with administrator permission.

its already running under admin
Processor:
Intel(R) Core(TM)2 Duo CPU T8300 @ 2.40GHz (2 CPUs), ~2.4GHz
Memory:
4094MB RAM
Hard Drive:
209 GB
Video Card:
NVIDIA GeForce 8600M GT#
and vista is 64 bit

Try running it under compatibility for Windows XP Service pack 2 or Windows 98, You can also try disabling visual themes, that might help. Oh also try updating your Chipset and Videocard Drivers. Also what Antivirus are you using? I've noticed Kaparsky and System Mechanic caused bsod's while gaming.

if its not a question of a overtly fragmented hardrive (if so defrag it), or the powersupply (a very underlooked part of a computer!, not strong enough might resolve in overheating! its not the fans, its the powersupply!)

if its pure software based...then try this...
It worked for me...I had issues to with grafix from the first starting area...
Type...

Windowskey + R (to get Run command)
type "C:\yourgamefolder\Messiah\MessiahD3D.exe -x"
the " -x" part will popup an window that will ask..

"Select Resolution"
800 x 600
1024 x 768
1280 x 960
1280 x 1024" <-- I picked this one

Then click "OK"

Now a new window pops up that says..."Messiah by Shiney Entertainment (c) 2000"
This is what I picked
Driver: (NVIDIA GTX 560Ti) my card. avoided the generic "primary display driver"
Device:Direct 3D HAL (very important!, otherwise might stutter, according to posts)
Mode:1280 x 1024 32 bit (this is the highest res I got out of it and it still shows the HUD! Yay!)

Let me know if this works for ya!

Btw Im on a Win7 Pro 64-bit, Intel i7 Quadcore, Nvidia GTX 560Ti Direct II CU, 8 GB RAM, Intr. sound card.
And it worked for me! Dont know about ATI cards...