php reg expressions

[eddy]

i have got this code for validating an email using regular expressions, it doesnt seem to when using php 4.2.3
does anyone know why

"^{([[:alnum:]]|_|.|-)+@([[:alnum:]]|.|-)+(.)([a-z]{2,4})$"}

thanks

[RedDragon]

no idea why it shouldnt work,
i am using this function

function isemail($var) {
	if(ereg("[A-Za-z0-9_-]+([\.]{1}[A-Za-z0-9_-]+)*@[A-Za-z0-9-]+([\.]{1}[A-Za-z0-9-]+)+", $var)) {
		return TRUE;
	} else {
		return FALSE;
	}
}