With all due respect we lost 58,000 troops in Vietnam, maybe we weren't prepared properly but we sure as heck aren't losing the same numbers of troops.
At the same point of time in the conflict we've lost
more troops in Iraq than we did in Vietnam.
Numbers are pretty worthless, however, as the troop levels were much lower at the start of the Vietnam War (meaning the ratio of deaths to troops is closer than just comparing deaths), and survivability for troops today is much improved with body armor and medical care (meaning many of the injured today would be deaths in Vietnam). Along with plenty of other factors, such as terrain differences and the amount of support foreign countries are giving the enemy.
It would be far more useful to address his specific concerns (in terms of prepardness and difficult in locating the "enemy.") rather than just throwing a number out there as if it invalidates any comparisons. I'd say the preparedness part is debateable, while the second is really the most accurate comparison to Vietnam that I've seen.