Accessibility Issues and compliance for serving advertising on web sites

Hi Guys,

We have a client who wants to take advertising on their site but also wishes
to remain compliant with regards to accessibility etc. The only offering
they have had from their third party ad sales house is to feed in adverts
from their ad servers via JavaScript which to my knowledge will give them
accessibility compliance issues.

Am I right about this one or are there any other ways of doing it apart from
running the adverts as external gifs and having a full description of each
advertisement written into the alt tag for the image source code?

Cheers

Stephen Morgan