It is possible to use an OEC demo to actively test DDE functionality. Excel trading and DDE function exactly the same between a live account and demo account on OEC Trader.
For the Username field, this would be the Username you use to login to OEC trader.
For Account, you can find this by glancing at the top right corner of OEC Trader or by opening the Account Summary page. The account name should be along the lines of DEMO******. Take a look at the screenshot below for where to locate your account name:
Simply just type in the Username and account name in the corresponding fields and you should be good to go!
Hope this helps,
Optimus Futures Support