Convert PHP ereg_replace to preg_replace

Question

I am having a little trouble converting the below regular expressions to the updated preg_replace function.

$string = ereg_replace("(a:http://)([a-zA-Z 0-9 \#\&\;\@\:\/\.\_\-]*)\|([a-zA-ZÄÖÜäöü 0-9 \#\&\;\@\:\/\.\_\-]*)","<a href=\"http://\\2\"&gt;\\3&lt;/a&gt;",$string);

$string = ereg_replace("(a:http://)([a-zA-Z 0-9 \#\&\;\@\:\/\.\_\-]*)","<a href=\"http://\\2\"&gt;\\2&lt;/a&gt;",$string);

Any help would be greatly appreciated.