Sometimes you'd want to install Windows from a bootable DVD but you just have all the Windows files... I mean, in my case I've got Windows 7 build 7048 (beta drop, but it does not matter), but I currently don't have its related ISO image. So, if I want to install a plain new Windows 7 from scratch (booting  & installing from a DVD), guess what you need?, right..., I want to create my own bootable Windows DVD.
In order to do that, we can use several Microsoft tools that come in AIK (Windows Automated Installation Kit), for Windows Vista or Windows 7 (the latest in my case).

You can download from here, for instance:

http://www.microsoft.com/downloads/details.aspx?FamilyID=4ad85860-d1f4-42a1-a46c-e039e3d0db5d&displaylang=en 

Needed Tools you can get once you install AIK:
- oscdimg.exe (usually you can get it from in "%ProgramFiles%\Windows AIK\Tools\x86 )
- etfsboot.com (This is the boot sector file will put into the DVD)

1.- COPY WINDOWS FILES TO A HARD DISK


Of course, you'll need all the Windows 7 or Windows Vista files. For instance, I copied all of them within C:\Win7_7048_EN\x86fre
You could even add more custom files, like drivers or whatever..


2.- GENERATE THE ISO FILE


Open a command prompt console (with Administrator's rights) and go where you have the AIK's tools. Then type the following:


oscdimg -n -m -b"C:\Win7 7048 EN\DVD Bootable Tools\x86_Boot\etfsboot.com" C:\Win7_7048_EN\x86fre C:\Win7_7048_EN_ISO\Win7_7048_x86_EN.iso

You'll get messages like the following:
OSCDIMG 2.55 CD-ROM and DVD-ROM Premastering Utility
Copyright (C) Microsoft, 1993-2007. All rights reserved.
Licensed only for producing Microsoft authorized content.
Scanning source tree (500 files in 49 directories)
Scanning source tree complete (810 files in 159 directories)
Computing directory information complete
Image file is 2825107456 bytes
Writing 810 files in 159 directories to V:\Win7_7048_EN_ISO\Win7_7048_x86_E
100% complete
Final image file is 2825107456 bytes
Done."


At this time you'll have a new ISO file for Windows 7 or Vista!!. :-)

If you want Windows x64, just use the other file types for x64, like:
oscdimg -n -m -b"C:\Win7 7048 EN\DVD Bootable Tools\x64_Boot\etfsboot.com" C:\Win7_7048_EN\x64fre C:\Win7_7048_EN_ISO\Win7_7048_x64_EN.iso

COMMAND'S MEANING:

-b points to the boot sector file location (etfsboot.com). This file will make the DVD bootable. Do not use a space between b and path!

Then, first path is the location of original Windows DVD files.

Second path points to the directory where the iso file will be created in.

-n makes it possible to use extended file names.

-m allows to create iso files, larger than CD format.


3.- BURN YOUR ISO FILE


Just burn your new ISO image onto a DVD media using any third party software, like NERO, ROXIO, ImageBurn, etc.