Before I am going to explain you about high level 
Testcases,I would like to share with you,what testcases we 
will cover under high livel test cases and low level test 
cases respectively.

Write all the testcases under high level TC,which can be 
covered the main functionalities like 
creation,edition,deletion,etc....as per prescribed in the 
screen.
Wrtie all the testcases under low level TC,which can be 
covered the screen,like input fields are displayed as per 
the requirements,buttons are enabled or disabled,and 
testcase for low priority functionalities.

Example a screen contains two edit boxes login and password 
and a pust buttons OK and Reset and check box for the 
label "Remember my password".Now let us write high level TC 
and low level  test cases.

HIGH LEVEL TC
--------------
1.Verify that User is able to login with valid login and 
valid password.
2.Verify that User is not able to login with invalid login 
and valid password.
etc...
..
..
3.Verify that Reset button clears the filled screen.
4.Verify that a pop up message is displayed for blank login.
etc...
etc..

LOW LEVEL TC
--------------
1.Verify that after launching the URL of the application 
below fields are displayes in the screen.
1.Login Name 2.Password.3.OK BUTTON 4.RESET button etc..
5.check box,provided for the label "remember my pwd" is 
unchecked.
2.Verify that OK button should be disabled before selecting 
login and passwrod fields.
3.Verify that OK button should ne enabled after selecting 
login and password.
4.Verify that User is able to check the check box,provided 
for the label "remember my pwd".
etc..etc...

In this way,we can categorise all the testcases under HIGH 
LEVEL and LOW LEVEL.

Please make comments,inncase if I am wrong.

u are perfectly for the above answer

low level test case: A test case with concrete 
(implementation level) values for input data and
expected results. Logical operators from high level test 
cases are replaced by actual values
that correspond to the objectives of the logical operators.

high level test case: A test case without concrete 
(implementation level) values for input data
and expected results. Logical operators are used; instances 
of the actual values are not yet
defined and/or available.

Hi Any one of u can tell me have u been tested DEX
Application (Its a ERP Package)my self  I am a ERP consultant.