I know lots of people opposed to the Iraq War are ever hopeful that this war will be like Vietnam. The Beatles will never get back together but the Beatles Experience works just fine.
But the Vietnam Experience is not on tour in Iraq no matter how much the antis want it to be true.
Let's look at one easily quantifiable element. In Vietnam as in Iraq, the helicopter was everywhere and a vital part of the war effort. Granted, with the plentiful roads in Iraq we are more reliant on vehicles than helicopters (and with car bombs, the terrorists too rely on roads as Strategypage has pointed out), but we use helicopters quite a bit.
So the recent loss of a helicopter with the loss of 12 Americans is tragic. It is at least the 23rd helicpter lost in Iraq since the invasion kicked off almost three years ago. Twenty-one of the incidents are listed here. Of those listed, 12 are combat losses (including one incident where gunfire was involved so I assume it is a cause even if it only caused the choppers to crash while maneuvering) and ten are accidental. One is unclear. So 52% are combat losses and the average loss per year is about 8.
Contrast this to Vietnam wherefrom 1965 to 1972 we lost (according to a site that I can't remember now--I just wrote down the numbers) 2,076 helicopters in combat and 2,566 in accidents, or 580 per year. Forty-five percent of the losses were combat losses.
We do not face an insurgency in Iraq. We face a well-financed terrorism campaign. On occasion they get lucky and bag a chopper. But only real military units in the field can regularly shoot down aircraft as the NVA and VC did in Vietnam.