Help with project small, fast table

Hello,
I'm trying to build fast table in my database (in MsSql 2005), to store about 500,000 photos. I have application, to input them into table with 2 parameters: 'x' and 'y'. Table looks like this (columns):

x (int) | y (int) | pict (varbinary(MAX))

What I need is:
-possibility to fast input photos (without 'lag' while inputing pictures one by one. I need to have the same speed after 1000 pic. as after 50,000). Now it works good (index on 'y' and 'x'), but after few thousands of pics. it's slowing down...
-when completed, I need to find any photo by "x" and "y". It must be fast too

x and y are unique, but I don't create it's columns as unique, to avoid checking it while inputing (I know, there are no duplicates, so checking is unnecessary)

So, how to create fast table? Create any indexes? Or primary key? Or any other advices? I'm begginer in this issue, so I don't know, which table will be fastest one.

you should create Non-clustered index on both the column i.e X and Y.

I've tried this, but It seems to slow anyway.