I realized that the "Flags" variable needed to be a VT_I4 type, and this is not done automatically in VB/VBScript, so you have to do a manual conversion with the CLng function, I.E.:
const navOpenInNewTab = &h0800
Set oIE = CreateObject("InternetExplorer.Application")
oIE.Visible = True
oIE.Navigate "http://msdn.microsoft.com", CLng(navOpenInNewTab)
If you don't convert it, it'll be ignored, and you'll be left without a clue as to what went wrong.
-- Good catch! Apparently, only VT_I4 is recognized by the InternetExplorer automation object. If you are using the WebBrowser control, both VT_I2 (Integer) and VT_I4 (Long) types are supported. (jsudds)