How in a real time system landscape exist ?

Hi,

I have some confusions over landscape of SAP XI....can any one please help me to understand the following

1) How a typical system landscape for integrating a "File server" to SAP R/3 ( Appl.Server < 6.4)

Are we intall a stand alone SAP Web AS seperatly for SAP XI on which we install XI ?

or

we upgrade the application server of SAP R/3 to SAP Web AS 6.4 and on

the top of it we install XI server ?

2) If we have the same thing with SAP R/3 with SAP Web App server ver >=6.4

Are we install a stand alone SAP Web AS separately for SAP XI on which we install XI ?

or

we use the application server of SAP R/3 i.e. SAP Web AS 6.4 and on

the top of it we install XI server ?

Thanks and regards

Mahesh.