Is there a motherboard on the market that has at least these features
1. Receives a 2.8ghz Pentium 4 chip
2. Uses the Intel 850E Chipset
3. Includes the LAN connection in the board
4. Has USB 2.0
5. Has a CNR port in addition to the PCI slots

I couldn't find a perfect match, but here's what I did find.


ALMOST WINNER
=============

MSI qualifies with the 850E Max (MS-6545)
http://www.msicomputer.com/product/detail_spec/product_detail.asp?model=850E_Max

Note: the USB 2.0 is optional


ALMOST RUNNER-UP
================

Gigabyte appear to have two that fit your criteria, on the left side
of this comparison chart:

GA-8IHXP & GA-8IEXP
http://www.gigabyte.co.jp/home/comparison_p4.htm

However, their pages for the individual motherboards either mention
850E or CNR, but not both. It could just be a case of not updating
their websites:
http://uk.giga-byte.com/products/8ihxp.htm


LOSERS
======

ASUS do not appear to have one.

AOpen have motherboards that would qualify except their USB is only
1.1, not 2.0
http://www.aopen.com/products/mb/RDRAMSK478.htm

DFI also fails to have USB2.0
http://sj.dfi.com.tw/product/productlist2.asp

Supermicro fails:
http://www.supermicro.com/matrix.htm

Soyo, ABIT and AMI also failed.

The Intel boards offer either LAN or CNR, but not both:
http://www.intel.com/design/motherbd/md2/md2_available.htm
http://www.intel.com/design/motherbd/mv2/mv2_available.htm


Search strategy

CNR motherboard "Intel 850E"
://www.google.com/search?q=CNR+motherboard+%22Intel+850E%22

The Intel 850/850E chipset uses the ICH2 southbridge, which has a USB
1.1 controller.  It is possible for motherboard manufacturers to add a
USB 2.0 controller, but that will increase the cost and design
complexity.

It does look like the MSI board has all of your desired features. 
Howevwer, you would be wise to ensure that both optional features (LAN
and USB 2.0) are available on the same motherboard before purchansing
it.  (I was unable to unzip their support manual, which probably
contains that information
http://www.msi.com.tw/program/support/manual/mnu/spt_mnu_detail.php?UID=345&NAME=MS-6545%20Ver2.0,
If you have MS-Windows on your computer you will have better luck.)

Here are some links you may find helpful:
http://www.intel.com/design/chipsets/linecard.htm
http://www.intel.com/design/chipsets/850/
http://www.extremetech.com/article2/0,3973,428010,00.asp

The Intel D850EMVRL motherboard qualifies all the factors.
Check out : 
http://www.intel.com/design/motherbd/mv2/mv2_available.htm