I had the same problem with my dv2000t. A recent patch to the alsa driver posted on the alsa-devel list solved it for me. I just downloaded the patch and ran it against the 1.0.14rc2 driver, compiled and after a restart the auto-muting worked.
If I remember correctly, I did something like this after downloading the patch (44604-001.bin):
tar -xjf alsa-driver-1.0.14rc2.tar.bz2
patch -p1 < ../../44604-001.bin
./configure --with-debug=full --with-cards=hda-intel --with-oss=yes --with-sequencer=yes
sudo make install
I might have had other options on the command line as well, don't remember.
Looking at the alsa-devel mailing list it seems like a new version of the alsa driver (1.0.14rc3) is out with this (and probably other) patch. Reading the posts on the list, it seems there are however some problems with compiling the driver.
Hope this helps you. I'm not 100% sure about the code above but it was something like that which I did. I still don't have the internal mic working, but haven't bothered to really look into it.
HP COMPAQ V3000 3240