The number of simultaneous connections for Windows XP Professional is 10, for Windows XP Home Edition it is 5.

To make the best use of these allowed connections, do not keep connections open when they are not needed.

If you seem to reach the limit already with lower numbers, your client computers may keep several connections open or previous connections may linger.

If you get this problem when trying to print, particularly if you get system error 71, see the following Microsoft Knowledge Base article.

Troubleshooting Server Message Block inbound connection limit in Windows peer-to-peer workgroup
http://support.microsoft.com/kb/328459/