OH HEY! I missed the part about the USB network card. In Windows XP SP2, enter this command
netsh wins reset
Then reboot. If that fixes it, look for anything that might have hooked into winsock: NewDotNet in particular is a nasty. It may also indicate a problem with your antivirus' proxy program, which should automatically reset after clearing the wins (in this context, this means "winsock") settings.
[EDIT]: You also don't always have to do a full reinstall. Sometimes WOW (Windows-on-Windows) install via the repair options (second repair in the Windows Setup, not the first which is the recovery console) is enough to fix things. Be aware, however, that doing this reverts your installation to the patch level of the CD being used, and more recently will actually break Windows Updates (there is a KBA which tells how to correct this problem.) ALSO, some keys don't work across patch levels, and you might especially have problems if you try to use the Dell Windows key. When in doubt, always use the CD which came with the computer.
