With/Without Autopostback in dropdownlist(Microsoft XMLHTTP ActiveX??)

Hi,

I have use the following approach to hide/show a textbox when selecting particular item in dropdownlist. By which approach to give the user more convinient to enter data?? I had try to use this twol approach but unsuccessful.

[Autopostback = False]
I need to visible a textbox and RequiredFieldValidator when user select the item in dropdownlist before click the submit button. The visible of textbox & Validator are set to false. I want to call function in client script(Javascript) to call out the textbox. For example, If select item "Other", then the textbox is visible to enter data. The control to validate of requiredfieldvalidator is set to this textbox. Other than that item will hide the textbox & validator. I using ASP.NET with VB to do the data entry form.
As I know, If we set server-side Visible property to false, ASP.NET will not render control, So, Anyone know how to solve it and give me some sample code.

[Autopostback = True]
If we use the autopostback, it is take time to refresh the whole page, because I have a lot of dropdownlist with textbox in page. I found some forum, they recommend to use Mirosoft XMLHTTP ActiveX to refresh only the object not whole page when using ASP.NET 1.X. I know this problem has been solved in ASP.NET 2.0 by Callback Manager, but currently I'm using version 1.1 of framework.
Lastly I'm very appriaciate for those who give me suggestion and help because I struggle this with long time.

Thank you very much.

Calvin