Ok, I've sorted it.

Just replacing line 333 in admin\includes\functions\html_output.php with the following worked.

Code:
// bof php5 fix - aclarke - 301206
    if (empty($default) && isset($GLOBALS['$name'])) $default = stripslashes($GLOBALS['$name']);
	// eof php5 fix - aclarke - 301206
However, my admin menu still doesn't work when I'm on the links.php page.

Also, when adding a new link the category field is marked as required? Is this correct? I've just added a link without a category (as I have no categories setup yet) and it didn't nag me to specify a category.