A DNS lookup error

When attempting to access certain websites I get:

A DNS lookup error occurred because the request timed out during the lookup. (DNS_TIMEOUT)

Occurs in Int Exp 6, & Netscape both, with 2 sites in particular. Other sites seem ok. If I try accessing these from an alternate computor, laptop running thru a VPN connection via my employers system, works just fine.

Have cleared cookies, temp files, rebooted, etc.

Connected to net via Linksys router to Broadband (cable)
2 computors in household via same router,...same problem.
Seems inconsistant, after heavy duty clearing caches, running Norton Disk Doctor, considerable cussing, re booting, have had intermittant access for a day or two, then gradually slow down then finally quit accessing.

Both sites ping properly.

Any ideas appreciated.

Bruce

 

Which operating system?