if you see it in your stats, are they 200/304 successes? or 403s? There is an addon that they use for IE and can use for firefox that blocks referrers and sends an empty referrer, allowing them to still post their entries, but, surfers without those addons will surf galleries that have tons of 403 errors.
If it is in your stats, you can be somewhat sure that they aren't hitting .wmv files because Windows Media doesn't send a referrer.
Code:
RewriteEngine on
RewriteCond %{HTTP_REFERER} (fusker|fukser|fuskem|eonpal) [NC]
RewriteRule .* - [F,L]
is a little kinder. You can add more url 'pieces' inside the () as long as you separate the phrase with a |. The above code matches if it finds fusker, fukser, fuskem or eonpal in the url.