Two separate queries.
I don't use PHP, but it will be *SOMETHING* like this:
$r1 = mysql_query("SELECT * FROM updates ORDER BY date DESC") or die(mysql_error());
$r2 = mysql_query("SELECT images FROM portfolio ORDER BY RAND()") or die(mysql_error());
while ( $rows1 = mysql_fetch_array($r1) )
$rows2 = mysql_fetch_array($r2) or die(mysql_error());
$image = $rows2["images"];
... now output info for one record from $rows1 ...
... including that image from $rows2 ...
CAUTION: If you don't have at least as many images as you have records in UPDATES
table, you will run out of records from $rows2 before you get to the end of $row1.