Since I had all my problems installing Ultrapack 3RC4 and Dark Blue World and I used more than my share from the "how to"s here at GoG, It seems to me that it is proper to share my experience.

a foreword: AFAIK, Ultrapack is a well balanced pack honed especially for online fighting, while DBW is a more complete and historically accurate single player experience; it can be installed as a standalone, if i got it right, but Ultrapack adds so much that it would be crazy not to install it.

Things to download:
1) IL2 AND the downgrade to 4.10m patch from GoG
2) patch to 4.10.1m ( yes it is needed... I mean, really, really needed) at this link:
http://www.mission4today.com/index.php?name=Downloads&file=details&id=4044
yes, you need to subscribe, but I didn't find another place from which to download the file. The source of the link is here, just in case you need to apply another patch:
http://www.sas1946.com/main/index.php?topic=8528.0

3) In am unsure if this was necessary, but I did it and everything is working smoothly:
http://www.sas1946.com/main/index.php/topic,1531.0.html

3)Ultrapack RC4 from this link:
http://www.sas1946.com/main/index.php/topic,23452.0.html

4 optional) Dark blue world; select a source that suits you form this page:
http://www.sas1946.com/main/index.php/topic,21514.0.html

Now:
install Il2-Sturmovik
downgrade to 4.10m
upgrade to 4.10.1m
copy in the game directory the files downloadwd in the step 3; overwrite everything.
install Ultrapack 3.0RC4 (fundamentally extracting the files in the game directory)
start JSGME.exe and "activate" at least the "#UP# enable UP 3.0" mod;

run the game exe; it should appear a window, in which you can select "ultrapack" as mode; open and save also the configuration menu, in order to have a saved setup, then click on start and see if everything is ok.

If everything is fine, exit and remove from JSGME the "#UP# enable UP 3.0" mod and install also the Dark blue world copying the files in the game directory;

open again jSGME and this time add ONLY the DBW files (at least part of them).

Then open the Il-2 selector.exe in the game dir, press the change settings button and select as "game type" Dark Blue World". start the game and see if everything is OK.

If you want to activate the Widescreen option ("wide ecran" something), do so in the JSME (remember: if you use DBW, NEVER, EVER activate ANY UP mod ad vice versa!) and then go in the config.ini and punch in the values most appropriate for your system; mind you, don't look for widescreen in the menu, but in-game.

If everything works fine and you are in awe gaping at the staggering amount of usable planes, consider to drop by at SAS forums and at Ultrapack site and say thank you to the fine people that improved what already was the best sim for WWII war planes an transformed it in an unsurpassed masterpiece.

let me know if everything is clear!

Great post - and sorry to revive it years later but the links still work - and with the recent IL-2 sale and the attractive WW1 era DBW mod (DBW 1916) still around, this was a much needed and useful thread for me to find. Thanks.

Couple of extra points - one might want to explain what JSGME is to the uninitiated - it's a generic mod enabler, you have to install it's exe into the game's main folder. This enables you to install mods into the game but I'm sure there are tutorials elsewhere online. I got my free copy of JSGME v2.6 from the softpedia website. Secondly, the GOG offline files also include the earlier v4.10 version so you prob don't need to downgrade before upgrading to v4.10.1. And lastly the versions of Ultrapack 3.0RC4 (more often called UP3 RC4) which I found online (like your link) already come with Direct2Drive included so do you don't need to separately download it.

Yes, there are other options to mod IL-2 1946 - look up CUP (and it's successor, BAT) via the SpecialAirService (SAS) website, through which you can install "Dawn of Flight" which is a sort of successor to DBW (actually just DBW combined with another mod I think). Those alternatives also cover more eras from 1906 right up to 2006! - but both those alternatives are mega-mods which require a massive amount of extra downloads (especially BAT which is an extra 60gb or more) and are not designed for noobs at all - even their install guides (especially BAT) assume a working knowledge and experience of older versions of them etc. (They want you to suffer like they did I guess..).

To give a prime example of this, even though I've been gaming and modding since the 1980s, I was totally lost as someone new to modding IL-2 as there are literally zero help pages for dummies - I was only aware of DBW as a WW1 mod, but it now appears to me that what many WW1 gamers call DBW is actually DBW 1916, a submod of DBW. Anyway, it seems DBW 1916 (v4) needs DBW (v1.7) and v4, along with some instructions, can be found here:
https://www.sas1946.com/main/index.php?topic=26088.0

So, to recap. For DBW 1916 you need:
1) IL-2 1946 at version 4.10
2) the patch to upgrade to 4.10.1
3) JSGME (to install your mods)
4) UP3 RC4 (an ultra pack for IL-2),
5) DBW superpack v1.7 (which seems to be a great WW2 mod).
6) DBW 1916 v4

If you're interested in DBW (which also has a Spanish Civil War submod, etc), check here:
https://www.sas1946.com/main/index.php/board,192.0.html

But you'll notice there's no mention at that DBW parent page of the DBW 1916 submod! Oh, I just wish there was an ounce, somewhere please, of the amount of help and clarity for IL-2 modding as there is for literally every other major game I've ever tried modding. Coming to it as a noob it's an absolute bloody nightmare.

Anyways... wishing you all clear skies, unjammed guns and a safe landing.