Every election is going to have some dirty tricks. Some are actually rather minor and I consider them to be "fair game," though not necessarily desirable or productive. So, the much-hyped story of some Dean campaign workers showing up at Kerry headquarters and pretending to be undecided Iowans is to me much ado about (mostly) nothing. Of course, it's perfectly fair and reasonable for the other candidates to try and raise a stink about the issue.
The more serious charge about Dean campaign workers coming to Iowa to actually participate in the caucuses is also a dirty trick. Overzealous supporters are capable of anything, I suppose, but there is of course no evidence of any kind of organized effort to do this. But, making the accusation casts doubt on what Dean and his campaign are doing.
The most serious dirty trick, to me, is anything which uses dishonest information to try to discourage people from heading to the polls. So, these reports that someone is doing just that to New Hampshire voters are rather disturbing. Of course, this kind of dirty trick can work both ways - if true, it could be Dean campaign supporters doing nasty things, or it could be other people trying to make the Dean campaign look bad. I'm not endorsing either view here - of course I have absolutely no idea.
But, more generally, in the next few weeks we're going to see/hear about a lot of these things. I would suggest that no matter whose campaign you support you take them all with a grain of salt and not jump to use them as ammunition. I'm not saying that one shouldn't be critical of some of these things if they're true, but there's generally going to be some doubt about both the truth and origin of any of these things.
...Josh Marshall comments on the weirdness of the ARG information. Perhaps an enterprising journalist whose first name is Josh and last name begins with M should contact them and get more details.
[edited - ARG doesn't use automated polls. ]