wierd dns lookup problem

Some of my internal network pings give a strange error message. If I
look for frontdesk ping will show "frontdesk.cisco [63.146.68.202]"
and then time out. That IP address isn't close to anything having to
do with the system, not inside or outside addresses or dns. Other
inside searches work fine. When I'm having this problem I also can't
get to some internet sites. I might get to google but not yahoo. I can
even ping yahoo, get the ip and try to go directly to it and IE
eventually times out and fails.

Here's the setup. DSL, a modem/router, another router (the cisco),
then a switch and an internal peer-to-peer network. There are two
routers because the first one gives guest access to the internet while
the second one protects the internal network. I've tried several
routers and types of routers to be the second one. I've tried every
concievable combination of dynamic or static dns settings for one
router or the other or both, or using the address of one or the other
routers as dns. Any of those combination seem to work for the most
part but with these odd errors. I do not have another dsl modem/router
to try, but if I just use it by itself it works fine. I've used this
two-router setup in a number of other locations with no problem.

Any ideas?
thanks