net send problem

Disable the Messenger service in the control panel under services.

ChrisV

check this out for a full review of options.

http://support.microsoft.com/default.aspx?scid=kb;en-us;330904

Here is MS' work around this issue for the web page, turn off the Messenger service. To do so, follow these steps:
Click Start, and then click Control Panel (or point to Settings, and then click Control Panel).
Double-click Administrative Tools.
Double-click Services.
Double-click Messenger.
In the Startup type list, click Disabled.
Click Stop, and then click OK.
Note If the Messenger service is stopped, messages from the Alerter service (notifications from your antivirus software, for example) are not transmitted. If the Messenger service is turned off, any services that explicitly depend on the Messenger service do not start, and an error message is logged in the System event log. For this reason, Microsoft recommends thatyou install a firewall and configure it to block NetBIOS and RPC traffic instead of turning off the Messenger service.
MORE INFORMATION
The Messenger service uses UDP ports 135, 137, and 138; TCP ports 135, 139, and 445; and an ephemeral (that is, short-lived) port number greater than 1024.

In addition to preventing net send messages, a firewall can also protect your computer from other malicious attacks over the Internet. These attacks can be designed to perform the following tasks:
Access your private information
Distribute software illegally by appropriating space on your hard disk
For additional information about this issue, visit the following Microsoft Web site:
http://www.microsoft.com/WindowsXP/pro/using/howto/communicate/version45/stopspam.asp