attachment page template? only show attachments for current post?

The attachment.php is a specific template in the WordPress template hierarchy. WordPress uses it for a specific purpose, and the default Loop just won’t do what you’re claiming it’s doing. (The behavior you’re describing would be analogous to the single.php template file looping through all Posts.)

I’m guessing your attachment.php template file has a custom Loop. As Baiternet asked above, can you post or link the markup of your attachment.php template file?