Frustrated by RegEx in PHP

Hello all,

sorry to disturb you with this-
but i am not really good in regex and can't catch it...

I have to parse a html document, and want to replace a piece of this link:

<IMG ID="Bild4" height=30 width=209 
SRC="./assets/images/Werbung_oben_header.gif" VSPACE=0 HSPACE=0 
ALIGN="TOP" BORDER=0 ALT="">

It shall be:
<IMG ID="Bild4" height=30 width=209 
SRC="./nts/templates/images/assets/images/Werbung_oben_header.gif" 
VSPACE=0 HSPACE=0 ALIGN="TOP" BORDER=0 ALT="">

My regex expression must not care about case sensitiv, should start it's
work when it finds a <img and stop when the > is coming- so that it is
guaranted that only image-src's will be changed.
The ./ before some Pathes must be cutted of and replaced with my path.
Of course, when ./ is not written by the designer it must match too.
And, when for example attributes are in total lack of order, the regex 
must accept this :)

I have allready started, but nothing of my helpless trys works.

$tpl_source = preg_replace( "=<img\s.+src\=\"(\.)/.+\"\s.+", $url, $html);


$html is my html-document, the $url my extension.

I this possible? Could someone help me plese?
This would be really great!
So, thanks for reading this!
Have a nice day,
Chris.