Xming is an X server which can have individual X applications remote displayed to it. However I do not believe it's capable of accepting an entire desktop as a single element that's remote displayed to it.
Usually you have to use a different protocol for this, XDMCP.
XDMCP is a remote desktop protocol. With XDMCP, one computer A running X11 can connecting computer B running X11, and interact with computer B as if one were physically at computer B. XDMCP is integrated into X.org, the default X11 server in Ubuntu. XDMCP also needs to be implemented by the display manager.
Further down on this same page they discuss using Xming with XDMCP.
Xming is an X server for Microsoft Windows. Officially it supports Windows XP, Server 2003, and Vista. It appears to work on (64-bit) Windows 7 as well.
It supports being an XDMCP client, but this is not officially documented in the manual.
First download it from sourceforge and install it.
You can then connect to server with IP address of 192.168.1.101 by running the following command on 32-bit Windows:
"C:\Program Files\Xming\Xming.exe" -query 192.168.1.101 -clipboard
or on 64-bit Windows
"C:\Program Files (x86)\Xming\Xming.exe" -query 192.168.1.101 -clipboard
You can replace the IP address with a hostname as well.
Please note that many of the other command line switches in Xming do not work with -query for XDMCP. This includes -wgl for 3d acceleration.
Please note, do not run any 3d programs as that program will crash, leave a black box for the area of the session, and you will have to kill the 3d program manually. The default kill level does not work, although kill -5 does.
To make connecting to a specified server more convenient, you can browse to the (regular) Xming shortcut in the start menu. Copy and paste it to the Xming folder. Then edit the copy of the shortcut by right-clicking and going to properties. Edit the name under the general tab to be whatever you want. Edit the target under the shortcut tab to be what is listed in the above examples (remove the default switches like -multiwindow .)
As an alternative to the above, you might want to look at using VNC instead. VNC will allow you to remotely connect to the Linux system's desktop and interactive with it. You can install a VNC client on your Windows PC, such as UltraVNC, and a VNC server on your Linux box. Typically this can be enabled, for example, under GNOME through the menu pulldowns: System --> Preferences --> Remote Desktop.
With remote desktop sharing enabled you can then connect to this desktop using UltraVNC.
Which to use
Of the 2 I would recommend using VNC over XDMCP. VNC is slightly more secure & performant, and can be carried over a SSH connection so it can be made more secure. XDMCP could be carried over SSH but in general, most of the X11 protocols were never really meant to be carried over the network. Then can be used in a LAN setting getting reasonable performance, but never should be carried over the WAN.