I have developed a system which i want my client to use for trial purpose for 1 month. i want a software or an idea to time the system for that period after which it should cease to work. can somebody help me?

Just some hints:
1) Compare the creation date of the executable file to the current one.
2) Create an entry in the rgistry with he installation date an chage the permission to this key to r3ead only.
3) Use a property setting in your application to be filled if empty with the current date, and another with a number of times being used. At each start, verify the date and decrease the number of remainig trys to execue.
4) Create a hidden system file in the user roaming with a name starting and ending with $ holding an encrypted value corresponding to the first usage date.

etc.

Hope this helps