help needed

hello everyone..my self nilesh and i m new to vb.net and developing one
web application..and now i've one problem...the problem is like that i
m creating one datatable and in that user will add new record by making
dataentry and that record is stored and when make dataentry second time
the first one will be overwrited...here is the coding that i did..plz
see it
dim dt as new datatable("Book Order")
dim dr as datarow=dt.newrow()
dt.columns.add(new datacolumn("Id",gettype(string)))
dr.("Id")=txtid.text
dt.rows.add(dr)
datagrid1.datasource=dt
datagrid1.databind()
here i show the coding for only one column i did the same coding for
all the column...hope
u'll get the solution for my problem..tell me what should i do?
and i also want to use the messagebox in my application so how can i
use it?i think for that i've to use javascript then tell me the coding
for that s i don't know that..and i also want to use the menu so how
can i do that?should i use style.css or something else?
and plz keep in mind that i can't use control in my application s the
company for which i m developing the application is don't want it..