Just to let you know that after a few weeks spent on searching the net for the best possible information (including tens of pages on this forum), followed by a very painful mining for the appropriate ATI/AMD "AGP Hotfix" drivers, (I can't believe that AMD didn't bother to keep an archive for their legacy products). So after navigating from the most obvious to the most obscure sites downloading copies (or their interpretation of the originals). Then a trial and error hazardous process of install, test, tweak uninstall started and ending for a good number of times in CTDs and/or the dreaded BSD (not counting the risk of inserting malware or other doubtful features in your system.
Finally I came to the same conclusion that I found on a Mike post more than ten year old: while there is no doubt on the quality of the AMD graphics and also the excellent quality/cost relation of AMD GPUs, for IL-2 Nvidia cards are much easier to handle, to configure and to provide good results. If Mike had pointed me to his very old post I should have thought three times before embarking in this errand.
Luckily I am an old man with time to waste and able to enjoy this type of research. Just not to completely give up on the subject I can say that the card is actually nice and works well for plenty of other activities than IL-2. In my humble view the best drivers that sort out the "infamous perfect mode problem" are the ones between Catalyst 11.1 and 12.3 (the last semiofficial release for an AGP card on XP system) even though with jester tricks you can install up 13.4 and even 14.5 however as to be expected the higher you go the most resources will be demanded from your system and just forget about a miserable P4 3.06Ghz and 2Gb RAM.
The beautiful graphic will be delivered at trickle FPS and punctuated by "the memory at 0x00000019 can't be read" or similar sudden freeze at the time of landing after bagging two veterans and one ace and followed by a frantic Ctrl+Alt+Del to avoid system reboot.
There are black magician arts invoking the miraculous effects of atioglxx.dll that unfortunately never worked for my system even though i tried one by one in all possible positions and conf.ini tweak.
Finally I am slightly better off now that when I started: the system works reasonably, I have acquired a reasonable knowledge of vintage ATI GPUs, appreciate again the easiness of working with XP and maybe still with the energy to now follow Kelso (and Mike 12 year younger) advice.
Cheers and thank you for your support It has been an intense three weeks of fun