strange problems with Internet connection

[Lutzer]

I'm using Ubuntu Breezy on my MSI laptop which has an integrated Realtek
8139 Ethernet card. The Internet connection is realized through a
DSL-router which provides DHCP. After using the Internet for some time
(varys between some seconds and some hours) the resolving of DNS fails
regularly. Most of the time I can fix it immediately by executing
"dhclient eth0". After some time it fails again. ping to my router and
traffic without DNS quering (e.g. filesharing) works without problem.

I guess it could be a Ubuntu specific problem because
1. Other Kubuntu and Windows PCs in the same network does not have any
such problem
2. I had the same problem with another laptop (IBM Thinkpad) at another
house, another network and another ISP but with Ubuntu Breezy (probably
Hoary as well)

any ideas are welcome! Lutz