Demul isn't really working for me... help

Alright… i’m trying to play HNK and basically all the graphics on the screen keep flashing… and runs @ like 40 fps.

Are there plugins i need to get in order for it to graphically look alright and speed up?

my computer’s stats:

dual core 2.3gz
2 gigs of ram
a decent graphics card (radeon 512 mb i think)

i run on win vista… maybe thats the problem?