good ideas. While I was waiting on some replies lastnight I decided to try something for myself.
What I did:
I used daemontools to mount the CD images.
Extracted all of CD1 in a folder
Then I extracted everything from the other CD's(including playdisc CD) except the 2 autorun files and help folder you can't copy these or the DVD won't load up automatically when you put it in(make sure to copy the ones from CD1 though we need those).
When it asks to overwright everything do so.
After extracting all the CD's to one folder load Nero
Go to make data DVD add all the files(not the folder) from the folder to nero
Important, name the DVD to UT2004_CD1 if you don't the DVD will not load up asking if you want to install UT2004. You can still install by going to my computer and clicking the DVD/setup.exe but who wants to do that.
I didn't touch anything else in Nero just went to burn after naming the DVD. After burning it popped out and I put it back in. Loaded up asked if I want to install UT2004, entered the key and it installed completely without asking for any CD's or with any errors. I love it because swapping 6 CD's sucks.
The game will not load without the original CD or a CD crack. But the latest patch fixes that anyway. I would bet you can do this with Doom III or any other multi disc game aswell just do it the same way. I think when a certain file can't be found(during installation) it then askes for the 2nd,3rd,4th,ect CD's to look for that file. But if all the files can be found it doesnt need to ask for them and goes on.