on Vista?
That's quite possibly true for your specific needs, but you can't make it a general statement.
Mac might undercut but I KNOW I can get an out of the box unit for my staff without any hassles. Also I don't have to hire a computer person to put the new computer on the network.
A Mac is a lot easier than a PC for that. It's also easier to set up, and especially maintain, servers. The tools that come with OS X Server are like getting a 2003 box and buying a bunch of extra management software. Plus enterprise management software for OS X tends to be cheaper (the PC tools to implement Apple's Remote Desktop or XSan are very pricey).
When the super majority of the market is Windows based then that is where the least costs lie.
Then how can Macs undercut other OEM PCs?
If I go to a conference, the hotel business center runs windows computers not mac.
That might be a specific reason for some people to get a PC, but it doesn't apply to most (especially those who bring their laptop).
Once the mac computers start selling Vista installed and running top of the line intel chips then perhaps Mac would be viable.
They're already using those chips. As for Vista, what OS X user in his right mind would want to downgrade? He already has a mature version of what the yet-to-be-released Vista wants to be (and may be in a few years, but by then OS X will have moved on).
on Vista?