Weird artifacts and Frame Independent Movement

Greetings. I have two problems here.

First off, I'm using OpenGL with SDL.

The first problem are weird lines around the transparent PNG picture as shown in the screenshot:
[attachment=10761:screenshot.png]

This is the PNG picture:
[attachment=10762:catanimate.png]

How can I make the lines disappear?

The second problem is Frame Independent Movement. I got it all set up, and I thought it worked until a lot of things went happening at the same time. At some places entities move very fast, at some very slow, depending on what's rendering on screen and what logic is currently happening.

Here is some code:

this is main.cpp:

Uint32 delta = SDL_GetTicks();
SDL_Event event;
g.OnInit();
while(g.running)
{
if(SDL_PollEvent(&event))
{
g.OnEvent(&event);
}
g.OnLoop(SDL_GetTicks() - delta);
delta = SDL_GetTicks();
g.OnRender();
}


and this is how the player, for example, moves:

x += xVel * (delta / 1000.0f);


Thank you for your help