The best way is to create a dual/multi boot system. Is much easier to start with an empty hard disk.

1- You need some software to create partitions. Use Easeus partition master. 2- Create a primary partition for your general use Windows. For Windows 7, 30 GB is ok.

3- Create a primary partition for your clean Windows. For XP64, 15 GB is enough.

4- Create the secondary partitions, D,E,F..., how much and with the size you want. Here you will install the programas. Never install programas in driver C, unless the installation software gives you no other alternative.

5- Install some software for multi-boot. This is the best way, one Windows partition will be hidden and the other Windows will not see that exist other Windows.

6- Select and boot in one partition, install Windows, drivers and apps.

7- Select and boot in the other partition and install the other Windows, drivers and apps.

8- Many programs once installed by one Window will not need to be installed by the other Windows, is enough to run them. Other you will need to install, so you will have two copies of the same app.

 

If you want to do this with a disk that already has Windows and apps intalled, is much complicated because you have to resize partitions, create new one, install the other Windows and if you had not done something like this before, I recomend you start with an empty disk so, if something goes wrong, you only need to start all again and nothing was lost.

Stupidity also evolves!