По дэфолту было:
Код:

RewriteRule ^([a-zA-Z0-9-]*)/([0-9]+)\-([a-zA-Z0-9-]*)\.html(.*)$ /product.php?id_product=$2$4 [L,E]
Ссылки переписал кириллические, с браузера копируются так:
Код:

/%D0%B2%D1%8B%D0%B1%D1%80%D0%B0%D1%82%D1%8C-%D0%BA%D0%BB%D0%B0%D1%81%D1%81%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D1%83%D1%8E-%D0%B3%D0%B8%D1%82%D0%B0%D1%80%D1%83/23-classic-guitar-classic-guitar-tenson-classic-guitar-tenson-f500-090-buy-classic-guitar-tenson-f500-090-kiev.html
Следовательно правило написал так:
Код:

RewriteRule ^([a-zA-Zа-яА-Я0-9\%\-]+)/([0-9]+)\-([a-zA-Zа-яА-Я0-9-]*)\.html(.*)$ /product.php?id_product=$2$4 [L,E]
Но не работает
На счет хедеров, то вот:
Код:

http://dommuzyki.com.ua/%D0%B2%D1%8B%D0%B1%D1%80%D0%B0%D1%82%D1%8C-%D0%BA%D0%BB%D0%B0%D1%81%D1%81%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D1%83%D1%8E-%D0%B3%D0%B8%D1%82%D0%B0%D1%80%D1%83/23-classic-guitar-classic-guitar-tenson-classic-guitar-tenson-f500-090-buy-classic-guitar-tenson-f500-090-kiev.html
GET /%D0%B2%D1%8B%D0%B1%D1%80%D0%B0%D1%82%D1%8C-%D0%BA%D0%BB%D0%B0%D1%81%D1%81%D0%B8%D1%87%D0%B5%D1%81%D0%BA%D1%83%D1%8E-%D0%B3%D0%B8%D1%82%D0%B0%D1%80%D1%83/23-classic-guitar-classic-guitar-tenson-classic-guitar-tenson-f500-090-buy-classic-guitar-tenson-f500-090-kiev.html HTTP/1.1
Host: dommuzyki.com.ua
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.9.2.12) Gecko/20101027 Ubuntu/10.10 (maverick) Firefox/3.6.12
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
Accept-Language: en-us,en;q=0.5
Accept-Encoding: gzip,deflate
Accept-Charset: ISO-8859-1,utf-8;q=0.7,*;q=0.7
Keep-Alive: 115
Connection: keep-alive
Referer: http://dommuzyki.com.ua/8-%D0%B2%D1%8B%D0%B1%D1%80%D0%B0%D1%82%D1%8C-%D0%B3%D0%B8%D1%82%D0%B0%D1%80%D1%83
Cookie: низя :)
Cache-Control: max-age=0
HTTP/1.1 404 Not Found
Date: Thu, 11 Nov 2010 21:33:05 GMT
Server: Apache
X-Powered-By: PHP/5.2.13
P3P: CP="IDC DSP COR CURa ADMa OUR IND PHY ONL COM STA"
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Keep-Alive: timeout=5, max=20
Connection: Keep-Alive
Transfer-Encoding: chunked
Content-Type: text/html; charset=utf-8
Работает так:
RewriteRule ^(.*)/([0-9]+)\-([a-zA-Zа-яА-Я0-9-]*)\.html(.*)$ /product.php?id_product=$2$4 [L,E]
Но неинтересно