I discovered after installing ME1 via Steam that I only had to run Steam as administrator once, after that first time I started the game I could reset Steam back to its vanilla compatibility (not admin) and the game starts and runs fine (so far). Having Googled I found a few forum posts mentioning this, but most places (including this Wiki) seem to imply that you need to leave Steam with Admin permissions.
Anyone else found that you only need to start Steam as Admin once? Or the opposite that you need to leave it as Admin all the time you want to run Mass Effect ? Not sure this should be mentioned in the Wiki page if common, but some people may well prefer not to have Steam run as Admin all the time