Your link didn't come across. But all you have to do is this:
1. Install Windows 7.
There's no such thing as an "upgrade" from XP - you get to install Win7 from scratch.
Use your XP partition.
At that point, you should have Win7 up and running.
2. You'll lose Grub.
That's just the way it is: Win7 doesn't play nice with other boot loaders (not even NT or DOS).
Your Ubuntu partition should be untouched.
3. Insert your Ubuntu Live CD.
Here's another link that might help:
Recovering Ubuntu AFter Installing Windows