adding images via post tags?

hi im creating a catalogue of products using wordpress and the company i am working for already has an existing website with over 1000 products (wholesale so not selling)
i am using csv importer to transfer as posts the products as that is how they are being uploaded atm however i am stuck with how to add the correct image to each post rather than adding the images all individually
the product tags have pictures by the same name so i was thinking if you could call the tag to display the related image
what ive got so far putting it in the post as i can use the importer to add it along with the products.
i have a php plugin installed and the_title displays correctly but single_tag_title does not it just returns blank;

<a class="lightbox" title="<?php the_title(); ?>" href="./wp-content/gallery/main/<?php single_tag_title(); ?>.jpg"><img class="alignleft size-full wp-image-99" title=<?php the_title(); ?> src="./wp-content/gallery/thumbs/<?php single_tag_title(); ?>.jpg" alt="<?php the_title(); ?>" width="150" height="119" /></a>

any suggestions or think of a better way to do it?
TIA
thebettertwin