this is a rather broad question, and doesn't have one very precise answer.
very generally, republicans are more "right-wing", favor smaller government and fewer social programs, less government regulation of business, and more conservative social values.
democrats are more "left", and tend to favor social welfare programs and more liberal social values.
for more relevant and accurate information, check out:
http://www.democrats.org/about/2000platform.html
and
http://www.rnc.org/Issues