Ok old bean
When you go to file save as you got a save and compress if you uses this the .
swf file should reduce.
Also make sure the graphic is a .
png as this handles alot better in flash.
Once you have done the save and compress go to publish and there are some options to reduce the image quality.
You have to do some playing around.
Flash in itself should compress the file. If the banner ad is going into a website which i imagine it is the .
swf will be server side and anything lower than 300KB should load really quickly within a site.
On my site i have an animation which is a 5MB graphic compressed down to 290KB using flash and it runs very quickly.
If you still stuck i grab some screen shots from my desktop and send them through.