Validation check for duplication key words

Dear All Members,
i am new in this group and start workin on vb.net. i make some small applications. in one application i need help some validation check about validation check.

for exampel, i enter a name in one text field in one row in the flex grid control and
the same name enter another row then he check first that name in the data base if
this name exist then he give this message that "name already exist".


so i need some code in vb.net that how i apply this key word check while i am
using database application or simple making two text boxes without connectivity
of database and check that name already exist or not.

I need some code related to vb.ent so i am waiting your response,

thanks in advance.
amir shahzad