On May 5, 2000 the planets Mercury, Venus, Earth, Mars, Jupiter, and Saturn will be more or less positioned in a line with the Sun. Additionally, the Moon will be almost lined up between the Earth and Sun. Although this has led to many dire predictions of global catastrophes such as melting ice caps, floods, hurricanes, earthquakes, etc. there is absolutely no scientific basis for these claims. The distance to the planets is too great for their gravity, magnetic fields, radiation, etc. to have any discernible effect on Earth. In fact, we won't even be able to see this alignment, as all the planets will be on the opposite side of the Sun from the Earth.
While each planet has a minute and virtually undetectable gravitational pull
on the Earth, with the planets on the opposite side of the Sun the force
from each body will actually be at its absolute minimum during the alignment.
And there is nothing "magic" about the planets being in a line, the effects
do not somehow multiply simply due to a geometric arrangement. For example,
the combined gravitational effect of all the planets together is much less
than the effect of the Sun or the Moon on the Earth. Depending on how
strictly you want to define "alignment", the inner six planets are aligned
every fifty to a hundred years or so. While unusual, such alignments have
happened in the past without any consequences. The planets are simply too
far away to have an effect on anything here on Earth - except our imaginations.
Gravitational Effects (or absence thereof) of the Alignment
The Bad Astronomy Web Page on the Alignment
Historical Alignments - Oklahoma School of Science and Mathematics (Courtesy Wayback Machine)
Interactive Planetary Orrery - Positions of the planets on any given date
NSSDCA Planetary page