Drop down list

Hi, im trying to create some sort of a drop down list for registering your date of birthday… But Im not quite sure how to tell PHP to post the selected value to mySQL…
This is what I got so far;

<form name="send" method="post" action="bday.php?update">
<select name="update_mybirthmonth">
<option value='1'>Jan
<option value='2'>Feb
<option value='3'>Mar
<option value='4'>Apr
<option value='5'>May
<option value='6'>Jun
<option value='7'>Jul
<option value='8'>Aug
<option value='9'>Sep
<option value='10'>Oct
<option value='11'>Nov
<option value='12'>Dec

</select> <select name="update_mybirthday">
<option value='1'>1
<option value='2'>2
<option value='3'>3
<option value='4'>4
<option value='5'>5
<option value='6'>6
<option value='7'>7
<option value='8'>8
<option value='9'>9
<option value='10'>10
<option value='11'>11
<option value='12'>12
<option value='13'>13
<option value='14'>14
<option value='15'>15
<option value='16'>16
<option value='17'>17
<option value='18'>18
<option value='19'>19
<option value='20'>20
<option value='21'>21
<option value='22'>22
<option value='23'>23
<option value='24'>24
<option value='25'>25
<option value='26'>26
<option value='27'>27
<option value='28'>28
<option value='29'>29
<option value='30'>30
<option value='31'>31

</select> <select name="update_mybirthyear">
<option value='1933'>1933
<option value='1934'>1934
<option value='1935'>1935
<option value='1936'>1936
<option value='1937'>1937
<option value='1938'>1938
<option value='1939'>1939
<option value='1940'>1940
<option value='1941'>1941
<option value='1942'>1942
<option value='1943'>1943
<option value='1944'>1944
<option value='1945'>1945
<option value='1946'>1946
<option value='1947'>1947
<option value='1948'>1948
<option value='1949'>1949
<option value='1950'>1950
<option value='1951'>1951
<option value='1952'>1952
<option value='1953'>1953
<option value='1954'>1954
<option value='1955'>1955
<option value='1956'>1956
<option value='1957'>1957
<option value='1958'>1958
<option value='1959'>1959
<option value='1960'>1960
<option value='1961'>1961
<option value='1962'>1962
<option value='1963'>1963
<option value='1964'>1964
<option value='1965'>1965
<option value='1966'>1966
<option value='1967'>1967
<option value='1968'>1968
<option value='1969'>1969
<option value='1970'>1970
<option value='1971'>1971
<option value='1972'>1972
<option value='1973'>1973
<option value='1974'>1974
<option value='1975'>1975
<option value='1976'>1976
<option value='1977'>1977
<option value='1978'>1978
<option value='1979'>1979
<option value='1980'>1980
<option value='1981'>1981
<option value='1982'>1982
<option value='1983'>1983
<option value='1984'>1984
<option value='1985'>1985
<option value='1986'>1986
<option value='1987'>1987
<option value='1988'>1988
<option value='1989'>1989
<option value='1990'>1990
<option value='1991'>1991
<option value='1992'>1992
<option value='1993'>1993
<option value='1994'>1994
<option value='1995'>1995
<option value='1996'>1996
<option value='1997'>1997
<option value='1998'>1998
<option value='1999'>1999
<option value='2000'>2000
<option value='2001'>2001
<option value='2002'>2002
<option value='2003'>2003
<option value='2004'>2004
<option value='2005'>2005
<option value='2006'>2006
<option value='2007'>2007
<option value='2008'>2008
<input type="submit" name="Submit" value="Update!">

if (($update_mybirthmonth >= 1) AND ($update_mybirthmonth >= 1) AND ($update_mybirthday >= 1) AND ($update_mybirthday <= 31) AND ($update_mybirthyear >= 0) AND ($update_mybirthyear <= $this_year))
include 'functions/DbConnector.php';
$birthday = "$update_mybirthmonth-$update_mybirthday-$update_mybirthyear";
mysql_query("UPDATE login SET birthday = '$birthday' WHERE username = 'Valerij'") or die ("Database error: ".mysql_error());
} ?> 

So basicly what this script does is… nothing… it displays the options, but then it does absolutly nothing… why?