You really should consider reading What Every Computer Scientist Should Know About Floating-Point Arithmetic. It's a 44 page paper, but you really should know it.

As the others have pointed out, there are arbitrary-precision libraries out there, but you're going to pay an efficiency price for using them. If you DO use them, make sure you check your results... In the case moritz demonstrated above, -Mbignum gives the correct answer, which you can check by reversing the operation:

$ perl -Mbignum -e'print 3.624920464504015567E+08 + -0.0002095444,"\n"
+'
362492046.4501920123
$ perl -Mbignum -e'print  3.624920464501920123E+08 + 0.0002095444,"\n"
+'
362492046.4504015567
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