Disable cell editing once the data entered

Respected Members,

I am developing a custom software in Microsoft Excel in 97-2003 Format. This program will determine the total and maximum running vehicle through graph. The program is completed but the thing is that, I wanted to disable a particular cell as soon as the data is entered in cell and pressed enter, means to stop the users to edit the value as soon as they press enter. So, can anyone just help me out, to solve out this querry? Any help, ideas and suggestions will be appreciated. Hope the best from your side.

Thanks in advance,

Regards,

Yuvraj Kumar, Asst. Manager (Information Technology)