You can run just about anything you want in an iFrame, but if  you want to take advantage of the DNN login, users, and built-in permissions, it is my understanding that you cannot use generic ASP.net "applications" (like the referred-to forums) as integrated DNN modules. 

I think that ASP.net defines the overall Microsoft language/environment, underwhich DNN works. Beyond that , I am not sure how to explain their relationships (not a "coder")

If you are looking for a robust DNN forum and cannot wait for the upcoming release, I can highly recommend ActiveModules' ActiveForums.
If you are looking for a free DNN forum, I can also highly recommend Presstopia's quite killer, free forum module.

If your community is centered upon a fully featured, totally killer, forum- I would look beyond DNN as your framework.

I think all the  DNN forums are bulky. I liked the old discussion module. I am currently using presstopia just because it allows anonymous postings. I am looking for a threaded module like this

Over 7,000,000 posts since March 2004.
		STICKY: ITT you tell me what you want	07/20/07	(335)
		STICKY: Public Announcement by rachmiel	07/20/07	(238)
		CALIFORNIA 2007 July MBE post-mortem:	07/26/07	(171)
		How much money does one need in the bank to retire well?	07/26/07	(95)
		PSA: Top 5% at a TTT doesn't mean jack elephant ****,	07/26/07	(24)
		How to best deal with lackluster grades at OCI?	07/26/07	(15)
		ITT: We post pictures of GWLAW23's bedroom	07/26/07	(11)
		Don't go to College become a millionaire guaranteed.	07/26/07	(4)
		I actually am starting to get the feeling that NYC is a TTT	07/26/07	(41)
		these guys put xoxo to shame in terms of cruelty to individuals	07/26/07	(25)
		Urban/Rural Battle, is the Republican Party Dead?	07/26/07	(5)
		What posters are the most made fun of?	07/26/07	(2)
		UVA law, awesome faculty, superior student body, integrated	07/26/07	(5)
		cum on me in this thread	07/26/07	(1)
		Old dried up whore past her prime, taking questions	07/26/07	(3)
		NYLS + Law Review = ?	07/26/07	(7)

As simple as that. The link I posted in my previous message shows forum based on ASP.NET, which have these kind of threaded forum. Particulary the first two.

So let me repeat this again gentle people, how can I use those forums with DNN? IFrame? How do i do it?

If Mitchel Sellers is reading this:

Can I do this with 3essential? I remember you said you have ASP.net websites with them? Please let me know.

Again, thanks for your time.