If you uninstalled TCP/IP and can't reinstall install it, use regedt32 to delete the following keys (and their sub-keys):

                              HKEY_LOCAL_MACHINE\Software\Microsoft\DhcpMibAgent                              HKEY_LOCAL_MACHINE\Software\Microsoft\DhcpServer                              HKEY_LOCAL_MACHINE\Software\Microsoft\FTPSVC                              HKEY_LOCAL_MACHINE\Software\Microsoft\LPDSVC                              HKEY_LOCAL_MACHINE\Software\Microsoft\NetBT                              HKEY_LOCAL_MACHINE\Software\Microsoft\RFC1156Agent                              HKEY_LOCAL_MACHINE\Software\Microsoft\SNMP                              HKEY_LOCAL_MACHINE\Software\Microsoft\SimpTcp                              HKEY_LOCAL_MACHINE\Software\Microsoft\Tcpip                              HKEY_LOCAL_MACHINE\Software\Microsoft\TcpipCU                              HKEY_LOCAL_MACHINE\Software\Microsoft\TcpPrint                              HKEY_LOCAL_MACHINE\Software\Microsoft\Wins                              HKEY_LOCAL_MACHINE\Software\Microsoft\WinsMibAgent                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DHCP                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\DhcpServer                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\FTPSVC                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Lmhosts                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\LPDSVC                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\NetBT                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SimpTcp                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\SNMP                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Tcpip                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\Wins                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WinSock                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\WinSock2                              HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\<NetDriver>x\Parameters\Tcpip
where <NetDriver> is the name your NIC and x is the number.

You may have to use Regedt32 / Security / Permissions to grant Administrator Full Control, before you remove the following keys:

                              HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\Root\Legacy_DHCP                              HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\Root\Legacy_Lmhosts                              HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\Root\Legacy_LPDSVC                              HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\Root\Legacy_NetBT                              HKEY_LOCAL_MACHINE\System\CurrentControlSet\Enum\Root\Legacy_TCPIP                              HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManServer\Linkage\Bind                              HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\LanManWorkstation\Linkage\Bind
Shutdown and restart your computer.

You should now be able to install TCP/IP.

NOTE: Don't forget to re-apply your latest Service Pack, after the TCP/IP install.