Yeah, I will post it here aswell, I was just so happy I forgot you for a while.
First I start with a rant so you can skip this if you want to go straight to the problem solving part. I can not believe it myself. I have literally been trying to solve this for a week. Perhaps 50 hours (or more) of pure trouble shooting, not much sleep, and reading a lot online but with no one being able to find a solution for HP Vista with IDT Soundboards. But now I am the God of Enabling Input Monitor on Vista, solely by myself, since HP or Microsoft where of no help whatsoever. However, I got clues about registry editing reading how to solve it on Realtek soundcards.
I called HP Sweden support, they did not understand why I wanted annoying feedback (the audio feedback that is what the mic and speakers create). So I mailed HP USA because I figured they would be of more help. It was like speaking to a child (However kudos to HP support Sweden e-mail support because they actually tried to understand my question and gave me answers, however they had no fix for it, but they could atleast explain to me they had understood my question and give me an explanation that Input Monitor was disabled on purpose on the Vista soundcards).
I kept getting advices from HP Support USA to do a complete reinstall of my computer etc, when I tried patiently to explain that was not the issue, and that they were giving advices on totally different subjects. Reading our mail conversation again I can't stop smiling (or is it sadness?).
I guess that is the CATCH 22 of support-business of the capitalist free world, because a talented support person will get promoted and stop doing these tedious support issues, and left in support are those who just can't help people out. Since if they could they would themselves be promoted and climb the ladder, and therefore stop working with actually helping people out, and round it goes, to eternity...
END OF RANT.
HOW TO ENABLE INPUT MONITOR FOR HP VISTA SYSTEMS WITH IDT SOUNDBOARDS (atleast on my HP Pavilion Dv7 Vista64 with IDT HD Audio card):
Read this carefully, since if you do not do as I did exactly there will be problems.
::::1:::: Open regedit and search for DisableMicInFromRender. Change it from 01 to 00. Or you can browse to:
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Class\{4D36E96C-E325-11CE-BFC1-08002BE10318}\0007\Settings\filter\Speaker1\
DisableMicInFromRender hex:01 change to hex:00.
RESTART COMPUTER.
::::2:::: NOW you have to downgrade your IDT drivers to IDT ID92HD71B7 Audio Driver. Go to:
http://h10025.www1.hp.com/ewfrf/wc/g...reg_R1002_USEN
and download the file sp39330.exe. I do assume you have the driver called sp41398.exe installed now. Do not install yet. Firstly, completely remove your old IDT drivers (do not blame me if something goes wrong, I am merely trying to help when Microsoft, IDT and HP does not give a s___). After this I think it is best to restart computer to be on the safe side.
THEN INSTALL THE sp39330.exe! AND RESTART AGAIN!
( For you others I found a forum thread with other Generic drivers you might want to look up if you do not have HP and IDT, scroll down and you find the links:
http://aumha.net/viewtopic.php?f=59&t=33686&p=203452
::::3:::: Go to Sound settings, go to playback\levels and you should now find the Mic volume option there, and perhaps muted. Unmute, raise the volume to max. (And check in Recording-settings that you have the mic turned on aswell.
::::4. Now here is the tricky part. It do work in mysterious ways, and it is very strange indeed. THIS IS IMPORTANT! I first did not get it to work, but I right clicked on the system tray, the IDT setting button. Right click on it, and choose the middle option. I do not know what it is called in English, but in Swedish it is called "Öppna minipanel för musikl". I guess it would be called something like "Open mini..." What it is is a small window called IDT HD Sound, and you can adjust your sound there.
WHEN OPENING it, my Input Monitor Mic started to spark AND IT WORKED! When I close it, the microphone stops working, but when I open it, it starts again! And sometimes when I restart computer it does not start at once. Then I have to do the Special move:
----Special move (Hopefully it works without this step for you)----
READ THIS: If it does not spark to life, THERE IS ONE IMPORTANT STEP TO DO IF YOU CLICK AROUND AND IT DOES NOT START WORKING!
Go to playback-settings in the system tray/Speakers/Advanced and uncheck the button in the "Exclusive mode" called "Give program that require exclusive mode lower priority" or something like that.
Then it mysteriously starts working, if it does not, go to Recording setting aswell and do the same thing there and press OK. And remember to keep the small IDT window open. Keep in mind it is not the big settings window. Rather weird I must say!
I really do not understand why it works like this, that one have to do weird stuff to make it work. Perhaps even some steps I described can be omitted but I can not figure out which step it is. IT IS REALLY WEIRD that you have to "trigger" the mic to work by doing some strange "Exclusive mode" setting and keep the small IDT window open.
Also, sometimes it keeps klicking on and off with intervals of maybe 1 minute. Perhaps some elite computer geek can explain this too me?
However, when you get the Input Monitor to start working it works until you restart, and after a while you start get the hang of how to make it spark to life. Perhaps you do not even need this last jerking around to get it to work. I hope so, just try to open the last small IDT window and perhaps that might work without these strange poking around I have to do to get it to work (sometime).
Keep in mind to keep the mic running so you hear when it sparks to life.
VENI VIDI VICI! Just took 50 hours or so...

I can answer questions here if it still does not work. Just read my steps carefully!
Ps. When I do know exactly what makes it spark to life I will post it here. I just got it to work and came here directly and posted due to my joy of success. Perhaps someone here can figure out and tell me?