IE and Firefox DNS Errors forcing reopening browser

Hello,

I am facing a peculiar issue. I use IE 7 / Firefox to browse the
internet. When I start the browser all seems fine but two / three /
five / ten minutes (no pattern, depends on the day) in to using it, I
get DNS errors. At this point I have to close the browser and re-open
it to continue browsing. The same issue exists in MS Outlook also. At
one time, I can have Firefox and IE open and the connection may work
in one and not in the other.

However, Google Talk remains continuously connected. Also, since other
PCs on my network work fine, the issue is not related to internet
connectivity.

Help, its frustating me big time..

Narayanan