I've seen lots of different "customized" versions of Windows floating around the interwebs....
They are versions of Windows that auto-install some apps (like FireFox or Office), some are pre-cracked, others come with custom themes integrated.
Personally, I would stay away from those. You really don't know what changes have been made and there is chance that some of those "customizations" could bring unwanted pests into your system.
If you want to always have a custom version of Windows ready to install, I would suggest you do the following....
1) Install Windows, get all updates, and register
2) Tweak, customize, change as you prefer
3) Do NOT install any drivers or applications (unless necessary) -- reasoning is that they are updated often and can come with major changes
4) Use imaging software such as Acronis (from its bootable media) to create a clean, installable image
For Apps, I use a service such as Ninite that will download and install my common apps such as iTunes, FireFox, and CCleaner.
Also, my system is setup so that all the things I want to save (documents, downloads, music, games that do not have to be installed to play) are all on other hard drives in my system. That way if I want/need to reinstall my OS I have very little to lose or that I need to backup.
The advantage to doing things this way is that you always have a clean and activated install of Windows on hand. Every few months or so I install the image, get any Windows Updates, and recreate the image so it's up to date.
Again these are my recommendations and I've done this successfully on many systems.
T
