Rodd, Here you have some code to test (it will require VFP 7+, I think):

try
	loWBEMLocator	= createObject("wbemScripting.SwbemLocator")
	loWMIService	= loWBEMLocator.ConnectServer()
catch
	loWMIService	= null
endtry

if not Isnull(loWMIService)
	loCSs			= loWMIService.ExecQuery('Select * from Win32_LoggedOnUser')
	for each loCS in loCSs
		try
			loUser	= Getobject('Winmgmts:' + Strtran(loCS.Antecedent, '//', '/'))
			? 'Domain     : ', loUser.Domain
			? 'Local?     : ', loUser.LocalAccount
			? 'Name       : ', loUser.Name
		catch
			? 'Error getting the User data'
		endtry
	endfor
endif

I this somewhat answers you question (Although I can not test for sure, I am only logged into my domain), the only problem is getting rid of the System accounts (Like SYSTEM, LOCAL SERVICE, NETWORK SERVICE, etc)