Ashish,
>>I don't want my user's to temper with it. Can I Encrypt a table when I am not using the application. When I go into the application Can I decrypt it.<<

There are several aproaches to acomplish this. You can encrypt in a table basis or on record or a field basis.
You can have your table encrypted on on your HD while not in use, decrypt it before using it and encrypt it back again when you close the application.
There is also a commercial "out of the box" solution by Xitech (the makers of Refox) that encrypts the data "on the fly".
Also if you are planning to use a dongle to protect your application, many of them come with a "wrapper" software utility that once applied to your exe encripts data on the fly.
Remember that whatever method you chose, there will be a small execution time penalty involved.
Hope it helps.
Roberto