I have been checking through some sites and it does seem doubtfull if indeed it can un-installed. Apparently its quite an integral part of Vista. I did find this page though which could be worth reading and it does actually give you instructions on how to remove it. Release Notes for Internet Explorer 7
It goes on to say that you have to type this in your 'Run' box and it will un-install..
%windir%\ie7\spuninst\spuninst.exe I did try it but with not much luck, maybe more reading is required. Hope this helps and good luck.