can I point 3 domain name to 1 ip address?

means use http header in IIS, that's my current solution, I can configure IIS by myself after I buy your service?

 

You cannot modify the headers in IIS. The only way to add additional domains to your hosting account, would be to add them as Domain Pointers which allows you to add additional domains to your hosting account.

Domain Pointer information: http://support.discountasp.net/KB/a131/domain-pointer-manager.aspx

 

does it need additional fee?

 

There is a $15 one time fee per domain pointer, and this will also allow you to use the Domain Pointer Email Alias

Domain Pointer Email Alias: http://support.discountasp.net/KB/a269/domain-pointer-email-aliases.aspx

 

well, is it Domain resgiter fee? I have the domain name already.

 

No it is not a domain registration fee. The fee is to establish the pointer service.