i've seen this problem twice now in the last two days, not sure what is causing the issue but i have found out what the fix is for it I think. the basic problem is IE stops surfing after a few minutes, also can happen in firefox, and problaly others and only happens in XP as far as i've seen so far
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here are the directions on how i ended up cleaning it. (WARNING changing things in the registry can cause your system to run unstable and or not run at all.) it can also be fixed by doing a flush and fill of windows but most people aren't willing to do that as an option.

delete all temp files, go to c:\documents & settings\"username"\local settings\temp\ delete all files & folders in there, also delete all folders and files under the "temporary internet" folder under local settings.

now go to the windows folder and delete all files and folders under the temp folder and temporary internet folder if they exist.

check and remove all possible spyware and adware. (not sure if this problem is caused by spyware and adware or what, but it was a step i did to clean the problem)

now go to command prompt and type "ipconfig /flushdns" with out the quotes.

now add the follow dwords into the registery. you can cut and past these lines into a notepad and save it as a .reg file to make importing easier.

[HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Servic es\Dnscache\Parameters]
"MaxNegitiveCacheTtl"=dword:00000000
"MaxCacheTtl"=dword:00000000
"MaxCacheEntryTtlLimit"=dword:00000000
"NegativeCacheTime"=dword:00000000
"NetFailureCacheTime"=dword:00000000
"NegativeSOACacheTime"=dword:00000000

reboot computer

and that should fix it. or at least it did for me. but it took me 4.5 hours onsite to get to the solution. if you have any other question you can PM me and i'll try to get back with you.