I'm using the jediSDL sprite-engine, so no opengl.

I think I found the problem too.
Due to some "too quick" programming on my side I failed to notice the 8-bit color display. (DOH!)
Do you guys know what the minimal color requirement for an alpha is? (I hope 16-bit is enough).

On the comps where I'm developping 16 bits color display is enough to run the game smoothly, A higher color depth causes lag.

Btw, another little question, not as high a priority...

I use the sprite-enigine as follows:

I have a surface.
On the surface I place a background (an image)
The sprite-engine is directly linked to this background.

I face one major problem with that.
When I give a single sprite the kill-command. The image sticks to the background eventhough the sprite is gone.
It's difficult to explain, but I hope the above is clear enough. Maybe this sprite-kill-thingy has something to do with the alpha problem