Why the heck do you download such crap? If you really need DOS there's a free and legal alternative:
http://www.freedos.org/

I'm surprised that people download executables from Gnutella. Did you visit the official site first to get a signature or checksum at least? If not, do you really think a software is safe if your virus scanner reports nothing? There's certainly no 100% safety or security but if you don't even try, you get none and deserve none. The problem though is, it's not just you, who's going to suffer but potentially millions of people who are going to receive spam (******, IM, Gnutella etc.) from your machine.

Edit: Oh, wow, you censor the short form of "electronic mail".