--------------------------------------
|   Binary   |   Hexadecimal   |
--------------------------------------
|    0000    |              0              |
|    0001    |              1              |
|    0010    |              2              |
|    0011    |              3              |
|    0100    |              4              |
|    0101    |              5              |
|    0110    |              6              |
|    0111    |              7              |
|    1000    |              8              |
|    1001    |              9              |
|    1010    |              A              |
|    1011    |              B              |
|    1100    |              C             |
|    1101    |              D             |
|    1110    |              E             |
|    1111    |              F              |
--------------------------------------

Ok, now, say you've got a hexadecimal number: B2C. Look at the chart and find the binary values for each of those hexadecimal values:

                           ---------------------------------
Hexadecimal  |     B      |     2      |     C     |
                           ---------------------------------
Binary               |  1011  |  0010  |  1100  |
                           ---------------------------------

Then, just remove the spaces between the binary numbers, and voila!, you've got your binary equalvalent of the hexadecimal value you started with.

B2C_H = 101100101100_B

I gotta give mad props to dann's E2 Offline Scratchpad for helping to make those charts.