How Should I Render Appropriate User-Entry For Getting User Data Dynamically?

Hi all

Recently i was asked to design and implement an On-line WebSite for a Shop Store.
I decided to define some Category for this Shop's Products such as MP3-Players,Mobiles,
Televisions,Monitors and so on....and then Assign each product to a certain Category.
Something like Amazon.Com , So i designed my Category and Product Table as follow:

Category Table
----------------
CatID    int Primary-Key
CatDesc  varchar(50)


Product Table
-------------
ProductID
ProductDesc
CatID

After that i noticed that each category has its own Fields and Property and sometimes some
categories have common Fields for example , Price ,Color are two Common Property or Fields
for all Categories that i mentioned earlier But , Size is a special property for only
[Monitor] or [Television] Categories and isn't useable for [Mice] or [KeyBoard] categories
for example. So i Added a table for Keeping each category's Fields as follow:

Category Fields Table
---------------------
FieldID     int
CatID       int
FieldDesc   varchar(50)
FieldType   tinyint --> 0=Numeric 1=String 2=Boolean...

After that i should save each Field's Value somewhere for each product so i added the
following Table(Product-Field-Value Table) for this purpose:

Product-Field-Value Table
-------------------------
ProductID
FieldID
Value

So far every thing is ok But i've faced with a new issue!!!.As you have realized so far , each product
belongs to certain category and each category has its own Fields List , in the other hand one category
maybe has only 3 to 6 Fields but another Category might has 10 or more fields,So my problem here is when
user wants to Add new product to Databse ,how should i get the Field's value for each product in an ASPX page ?
in the other hand i'm dealing with a dynamic structure as you can see, so how should i Render the appropriate
User Entries for getting Values of each product dynamically and then Saving these values in the Database?
what Asp.Net Components should i use for this purpose? Could anyone help me?

Thanks in advance.
Kind Regards.