Right, I've been trying to do this for a few days, searched plugins, mailed friends (well I used to have them until I began pestering them over things like this...) but I just can't find the answer. What I want to do is quite simply put a flash banner (I have uploaded the .swf-file to /uploads) in a sidebar with a link to the advertisers' site. Please help....

www.elektroretailmagazine.nl

You'd put the embed code into a text widget and place that widget in a sidebar.

See http://www.google.com/search?q=embedding+flash on how to embed Flash in HTML

Yes, I thought so as well, but I can't get it to work.
Ahhh, sometimes things like this can drive a person crazy, you know?

which sidebar, which location is it supose to be at? (i.e first widget, second, or it's between 'bowling for cash;' and 'eat at Joes')

right sidebar, second or third widget

I'm having the same problem, where I'm able to embed a YouTube video with no problem, but an SWF file - forget it.

http://www.equinecisers.com/wordpress/

I'd like to remove the YouTube video and replace it with a much better looking SWF file. Or an FLV file.