Question on Microsoft VPN IPSec solution

Hi, this is my case:

Imagine I want to minimize IPSec client management overhead. We have
thousands of users. Building client installers for the IPSec base solution we
have has consumed many hours of resources.

Anyone here has real experience using the Microsoft Windows(Windows XP or
Windows Vista) client to connect to VPN via IPSec? I am wondering how easy
that it is and whether that option work well?

Perhaps the Microsoft VPN client available with Windows may not get conneted
to other vendors such as Cisco concentrators, etc.

If you ever used the Microsoft IPSec VPN client solution, please tell me the
expectations as far as management overhead goes when compare to other non
built-in VPN IPSec clients (Cisco, Juniper, etc).