Question on image input in a image postformat

Btw, before I forget I had another question.

Is there a way I could have the image filenames that are stored on my server from the feed to have the name of the title post and the spaces replaced with hyphens and possible dots and comma’s to be removed.

So for example, if a title of a post that I am taking in is called:
This is a title post

Then i want the filename of the image that belongs to that post to be:
this-is-a-title-post.jpg

Right now the filenames fetch the POST id and end it with a -thumb.jpg (What about gif images? That would make them .jpg’s too then?) and I know this is handled in import_posts on line 52. But just not sure how I should take the approach to customize it.
the code for the people reading:

<br />
function setFeaturedImage($post_id,$url,$featuredImageTitle){  </p>
<p>    // Download file to temp location and setup a fake $_FILE handler<br />
    // with a new name based on the post_id<br />
    $tmp_name = download_url( $url );<br />
//								echo $tmp_name;<br />
    $file_array['name'] = $post_id. '-thumb.jpg';  // new filename based on slug<br />
    $file_array['tmp_name'] = $tmp_name;<br />

Perhaps have it echo the Alt text of the image? And then with a -mywebsitename instead of -thumb at the end of the filename.

I would understand if you can’t explain it all in straight instructional textbook style on how to achieve this with nicely baked codes. But any help is appreciated.