Your post really makes me ask the question 'Why?'
W7 is by far a better OS than XP. It has a compatibility mode which makes W7 behave as an earlier OS (you choose which one) if needed to run software which will not run in W7. In reality few programs fall into this category although some do.
When the beta version of W7 was released I made my PC dual boot with XP. I never used XP again despite it being available and when the retail version of W7 was released I bought a copy.
What you want to do is perfectly feasible but, I would humbly suggest, a complete waste of time and effort.
Also in my opinion W7 is one of the most intuitive and well laid out operating systems that MS have produced.