Other than that, seems your ISP (Wanadoo/IP2000) uses a rather weird network setup, involving two/three RFC1918 networks.
What you could try (if you have your own nameserver) is to forward all DNS requests to your ISP's nameservers. The fact that you get a quick reply to
www.sun.com is probably because that result is already cached as a result of your earlier visit to that site. Try a dig on some host you've never visited, and see what the response time is to that query. Then try with your DNS requests forwarded to your ISP's nameservers. If you have a lot of latency on your network, a typical external DNS lookup (non-forwarded), which can involve a lot of questions and answers (sometimes more than ten separate queries), suffers a lot.