New findings, you don't need to have the ad in 234x60 for it to show up, WLM stretches it
I've also set up some templates for the ads
WLM does stretch it but from my eye it seems to use the same image resizer from MS Paint, so bigger images can look a little crunchy.
As for the templates, I recommend increasing the size by 200% to work, then using a better program to shrink it as it will end up with a better appearance.
I can't find how would that help, honestly with all of the programs i have here also make shrinking look crunchy or bad, not to mention the small things become one pixel or die
Edit: I just tried it with images and basic shapes, seems to be a good way to do stuff, still wouldn't use it for something more complex