[Zope] Playing the Devil's Advocate: Why Zope?

[EvH]

Hi,

My dad is finally considering rewriting his business applications from VB 
to the web... and asked me to check out the different tools available. I 
know a bit about environments like Zope, OpenCMS, am currently checking out 
VB.Net or "simple" languages like PHP.

Could anyone experienced with those tools tell me why I should go for 
ASP.Net, or even what is the point of prefering more complex environments 
like Zope over PHP?

Any hint much appreciated
EvH.