Hardware Requirements needed to install R/3, XI and EP server.

Hello Friends

We have recieved SAP (R3 and Netweaver) software. We want to install R/3, XI server and also Enterprise Portal server on Windows XP.

What are the hardware requirements? I would appreciate if some one can give me details about the info on required memory, diskspace etc.,

Is it a good practice to install all these 3 on one machine?

Thanks

Ram