Yeah, as Adrian_T has said, the first number dictates whether the car was registered in the first half of the year, or the second (so to speak, as the halves are February to September and September to February). Currently, "0" represents the first half, and "5" represents the second. The second number dictates the year... "2" for 2002, "3" for 2003, "4" for 2004...
So "02" is the first half of 2002, "52" is the second half of 2002, "03" is the first half of 2003 and "53" the second half of 2003.
At the end of the decade, "0" and "5" (for first half and second half) will be replaced with "1" and "6". Therefore, "11" will be the first half of 2011, "62" will be the second half of 2012... and "69" will be the second half of 2019.
Simple, huh?