Well... I know how to get the Comments concatenated properly, but I'm not sure how to pull the customer. I'm also not sure if this will work in Access, because Access doesn't support stored procs.
DECLARE @Comments VARCHAR(8000)
SELECT @Comments = COALESCE(@Comments + ', ', '') + Comments FROM Customers
I'm guessing you'll have to do this for more than one customer, but all I can think to do is use a CURSOR for each customer, but I don't know if Access supports cursors at the moment.
DECLARE @Comments VARCHAR(8000)
SELECT @Comments = COALESCE(@Comments + ', ', '') + Comments
FROM Customers
WHERE Customer = @Customer (i.e. James, from the cursor)
Honestly, I think you're stuck doing this in PHP.
SELECT * FROM CUSTOMERS ORDER BY Customer, Comment
Then simply loop through the recordset and when the Customer changes, reset the Comments variable for the next customer.