A Cautionary Tale
I won't go into the details, but I was able to get the original iso files copied over to a different PC and used the software quoted above to create another AIO iso. This time I used the "automatic" mode where you do what brandonwh64 said regarding pointing the app to the two iso files (x64 and x86) and then pointing it to an empty folder to work in. It appears to have completed successfully. However... the resulting iso in "automatic" mode comes out to 6.45GB 
. That obviously won't fit on a single layer DVD and I don't have any dual layer discs. Besides that, the OP said the resulting iso should be around 4GB. Even better, the app decided that it would automatically delete the original iso files when it finished creating the new AIO iso... Great, thanks for that. 
Luckily I have a backup on my non-booting PC that I had to once again copy back to the working PC over the lan. So, the moral of the story is that you may want to be careful with this app. For me, I'm going to see if this 6.45GB iso will get me going. I put it on my 8GB thumb drive. I guess I will still need to go through the OP's manual steps however if I want to get a working iso that will fit on a single layer DVD. So much for simpler.
I too tried this tool. It seems to be fairly easy to use. I created an AIO iso using the Windows 7 Ultimate SP1 iso images from Digital River. I created the first one "manually" using the software mentioned in the quote. The iso came out at around 4-5GB, which seemed in line with what I was expecting. I copied it to a thumb drive using Rufus, which has never let me down. Everything appeared to work when I ran setup.exe from within Windows. I continued until the point of selecting a partition to install on. I then cancelled and prepared my PC for re-installation of Windows. I got everything ready, rebooted off the thumb drive, and proceeded. After I passed the step of reformatting the Windows partition, the installation failed. It said that something was corrupt or something along the lines of my installation media being f'd up. So great, I have a non-working installer and I've reformatted my partition.
I won't go into the details, but I was able to get the original iso files copied over to a different PC and used the software quoted above to create another AIO iso. This time I used the "automatic" mode where you do what brandonwh64 said regarding pointing the app to the two iso files (x64 and x86) and then pointing it to an empty folder to work in. It appears to have completed successfully. However... the resulting iso in "automatic" mode comes out to 6.45GB . That obviously won't fit on a single layer DVD and I don't have any dual layer discs. Besides that, the OP said the resulting iso should be around 4GB. Even better, the app decided that it would automatically delete the original iso files when it finished creating the new AIO iso... Great, thanks for that. Luckily I have a backup on my non-booting PC that I had to once again copy back to the working PC over the lan. So, the moral of the story is that you may want to be careful with this app. For me, I'm going to see if this 6.45GB iso will get me going. I put it on my 8GB thumb drive. I guess I will still need to go through the OP's manual steps however if I want to get a working iso that will fit on a single layer DVD. So much for simpler.
