Insert And Update Statements

Hello,

I am creating my companys' database and I have a small problem that must be
solved.

I have a pictures table:
PicturesTable
-------------
ProductID int ForeignKey
Picture nvarchar(30)
...

(A product can have many pictures & the ProductID is unique for any product,
but not for the table of pictures).

What I want to do is to somehow do a procedure to:
1) Check if any images (for a productID) exists in the table
2) if they do not exist then add the appropriate images into the table
3) if the images exist, then update the images with the new one that I have.

What I thought was to just delete all the images from the table for the
specific product:

DELETE FROM PicturesTable
WHERE ProductID = '10-11'

and then add the appropriate images:
INSERT INTO PicturesTable (ProductID, Picture)
VALUES ('10-11', 'Dir1/Pic1.gif')
INSERT INTO PicturesTable (ProductID, Picture)
VALUES ('10-11', 'Dir1/Pic2.gif')
INSERT INTO PicturesTable (ProductID, Picture)
VALUES ('10-11', 'Dir1/Pic3.gif')

but I do not like a lot this idea because if a user tries to read the pictures
for that product (at the same time I was deleting them) s/he would get
nothing. Is any other way that I can do it please?

I would appreciate it if someone answers me.

Yours, sincerely
Efthymios Kalyviotis
ekalyviotis@comerclub.gr