Hiya,
To include the flash banner you need to have your own server.
Let us assume you have a server with a domain name xyz.com and you create a directory named 123 in your server. FTP your flash banner to your directory.
Then add this piece of HTML when you are listing
Change the items in red with details of your flash banner.
If you want any further help mail me your flash banner and I will host it in my server and send you the code to copy paste in the auctions.
Regards,
Onesimpleman