DB Interaction

[RG]

I am using sql server 2005 as back end db. I am writting a concurrent
connection application where end users are updating, via a browser, the same
tables based on the data supplied by browser. It is possible that between
the times that a user pulls a row and updates that row, a concurrent user
may update it before him. Considering this, what is the optimal way of
handling database acces in these situations? What is the accepted approach?

Any info is appreciated,

Thanks in advance