Question : PING, DNS ok however neither browser works.

A clients home system stopped browsing a week or two ago. I was unable to get it going so brought it back to the office to work on. It is an XP Pro  SP1 box.

I'm able to ping to the internet, and am able to ping www.yahoo.com, thus DNS is working. However I can not get IE to work. Loaded Firefox 1.0 and find that also can not bring any web sites up. I reset the TCP/IP stack as mentioned in KB Q299357 but no change.

This client has had a bit of trouble with malware, both at the office and at home. On this home system I did install Spybot, Ad Aware and Spy Sweeper, tho none were able to update, and removed what I could.

I'm not certain this is a malware/spyware issue tho.  

Any thoughts on what might be blocking the browsers?

Answer : PING, DNS ok however neither browser works.

Still sounds like a firewall or something is blocking the port.  you can test this by typing:

telnet www.google.co.uk 80

from a command prompt.  If the commandscreen clears immediately then you are able to establish a connection via port 80.

If something (firewall or other program) is blocking port 80 it will think for a while & then print:

Connecting To www.google.co.uk...Could not open connection to the host, on port 80: Connect failed

If this is the case (as I suspect), I would first check your Windows XP firewall is not enabled. Then look for other firewall's in the add/remove program list, if you still haven't found what's blocking it I would run hijack this & post the output on here or better still a more adware oriented board.