Queries of the form
list($Parent, $CategoryName, $DBTemplate, $SortOrder) = mysql_fetch_array($catinfo);

no longer work (the exact same code with the exact same database does work with PHP 3.0.7).

I'll get an error such as 
Warning: Undefined offset: 0 in D:\IIS\template-demo\index.php3 on line 88

This only happens when a query returns a NULL in one of the columns. Removing the NULL takes care of this.

Switching to mysql_fetch_row still results in isset($row[0]) being false, requiring a change to something unwieldy like (isset($foo[0]) ? $foo[0] : "NULL");