I have made it simple for you:

$day1=$date["mday"];
$mon1=$date["mon"];
$year1=$date["year"];
$date=$day1.".".$mon1.".".$year1;

$query="insert into data (coll) values ($date)";

ERROR!!!!
(try to change the Mysql col. attr. to date)
ERROR!!!!
-----------------------------------------------------
ok try it in an other way....

$pattern="/(\d{1,2})\.(\d{1,2})\.(\d{2,4})/";
if (preg_match($pattern,$heute,$regs)){
echo $regs[3],"-",$regs[2],"-",$regs[1];
$date=implode("-",$regs);

$query="insert into data (coll) values ($date)";

ERROR!!!!
(try to change the Mysql col. attr. to date)
ERROR!!!!

---------------------------------------------------
ok try it in an other way....

$mon1 = substr($str,5,2);
$day1 = substr($str,8,2);
$year1= substr($str,0,4);

$date=$day1.".".$mon1.".".$year1;

$query="insert into data (coll) values ($date)";

ERROR!!!!
(try to change the Mysql col. attr. to date)
ERROR!!!!
---------------------------------------------------
Summery: 
php does not return real strings back and only structures or pointers to structures which make the live of the programmers harder than it is!

My solution: please create a blody simple function to convert dates to strings ... somthing like:

$string=DateToStr($any_date_format);

Eventually I'm very sorry folks I find PHP very nice but
PHP cannot give any basic solutions for dates
which will force me to use Microsoft ASP 

Yeh!, it is slow but at least it works