Using web forms for data entry

Hi everybody,
I am in the process of migrating to from VB6 to VB.NET.
My partner suggested to use Web forms for the entire application, i.e. data entry forms & reports. e.g. an Inventory application. According to him, using this approach would enable the users to use the application across branches of an organization, or if used only locally, could be implemented on an intranet. It seems that this is the way modern applications are designed and that Windows based applications have become obsolete.
So, I started making a Purchase Order entry module, which is a Master - Detail entry form using a Web form. But I realized that the events on the entry controls like text boxes fire only on clicking a command button. This I feel would be very inconvenient for the user as compared to a Windows form, because the user would be intimated of the data entry mistakes only on clicking the Save button.
Please let me know your views on this and advise me as to what I should be using and how to use it. Basically I want to know to what extent web forms should be used for data entry.