need help clean install

Hi everyone,
I have a done a clean install but only once a long time ago on my old desktop computer. I followed step by step instructions though and all went well. My friend knows I did this and asked me to do a clean install on her desktop XP Home computer, and I know it really needs it. My question is (because I've forgotten) do I keep the computer connected to the internet whilst going through all the instructions. I was going to bring her computer to my home to do it but I have an ADSL 2 modem and she has a Wireless modem so not sure if I can use my modem for the internet or even if I am supposed to be on the internet whilst installing XP. I know at some stage I have to connect her to the internet bus was thinking I could do that when I take the computer back. what should I do?, also can you direct me to somewhere where the step by step instructions are. I've googled this but found so many that seem to be involved and when I did it before it was quite easy but can't fremember if I was connected to my modem whilst doing it. I know of course that all her important files must be backed up which I will do with her so I know what she wants saved. Do you think I would be better off doing the clean install at her home especially if I have to be connected to the internet.
Many thanks for any advice.
Josey.