Mars is about 35 million miles from the
earth -- and was closer on Aug 27, 2003 than at
any time in the last several thousand years.
Over two years, the distance varies from about 39
million to about 240 million miles. If you have a
computer, you can download or purchase a program
which will tell you down to the nearest few
hundred kilometers for any time in last few
thousand years (or into the future...). Such
programs are mostly based on algorithms developed
by the Naval Almanac (which is now distributed on
a CD-ROM). (The Navy is into this historically as
star positions were used for centuries along with
a clock to find latitude and longitude at sea).
USNO web ephemeris (1 AU = 93 million miles)