A quick check of CyberSky tells me the best chance to see Mercury as an "evening star" is just beginning, and will last about a week. Right now, it's nearing its greatest "eastern elongation" - that is, catching up to Earth from behind - but as it does, less of its sunlit side faces inour direction.

On Monday (3/22/04) at sunset, Mercury will be west and a little north of a sliver crescent Moon.
elongation (angular separation from the Sun) = 16.8 degrees;
illumination = 67.9%;
magnitude = -0.9

Next Friday (3/26/04) Mercury will be passing its orbital apside not long after sunset.
elongation = 18.6 degrees;
illumination = 51.8%;
magnitude = -0.4

After that, Mercury gets closer to Earth, but shows a thinner crescent each night, and sets progressively sooner after the Sun. So, find the least-obstructed western horizon you can, and look for a tiny reddish unblinking object approximately 2/3 closer to the horizon than Venus. Binoculars will help.