如果你是要算連線數的話, 可以這樣下指令:

netstat -n | find "TCP" /C 這樣可以算 TCP 的連線數
netstat -n | find "UDP" /C 這樣可以算 UDP 的連線數

nadesico提到：
的電腦到底用了多少連線數，

可以參考使用簡易的指令(簡易不代表功能不好喔)
netstat
以下是WinXp下的CMD命令說明

<pre class="c" name="code">
NETSTAT [-a] [-b] [-e] [-n] [-o] [-p proto] [-r] [-s] [-v] [interval]

  -a            Displays all connections and listening ports.
  -b            Displays the executable involved in creating each connection or
                listening port. In some cases well-known executables host
                multiple independent components, and in these cases the
                sequence of components involved in creating the connection
                or listening port is displayed. In this case the executable
                name is in [] at the bottom, on top is the component it called,
                and so forth until TCP/IP was reached. Note that this option
                can be time-consuming and will fail unless you have sufficient
                permissions.
  -e            Displays Ethernet statistics. This may be combined with the -s
                option.
  -n            Displays addresses and port numbers in numerical form.
  -o            Displays the owning process ID associated with each connection.
  -p proto      Shows connections for the protocol specified by proto; proto
                may be any of: TCP, UDP, TCPv6, or UDPv6.  If used with the -s
                option to display per-protocol statistics, proto may be any of:
                IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, or UDPv6.
  -r            Displays the routing table.
  -s            Displays per-protocol statistics.  By default, statistics are
                shown for IP, IPv6, ICMP, ICMPv6, TCP, TCPv6, UDP, and UDPv6;
                the -p option may be used to specify a subset of the default.
  -v            When used in conjunction with -b, will display sequence of
                components involved in creating the connection or listening
                port for all executables.
  interval      Redisplays selected statistics, pausing interval seconds
                between each display.  Press CTRL+C to stop redisplaying
                statistics.  If omitted, netstat will print the current
                configuration information once.

另外，如果你想用美美的視窗工具，可參考：
http://technet.microsoft.com/en-us/sysinternals/bb897437.aspx

netstat 確實是做的到
但我都是用個小工具搞定
TCPView
很好用的
自已上網隨便找就下載的到

超強的軟件 TCP-Z，順便幫你的 TCP/IP 連線數改掉了。