If you are posting to a different page then it probably is best to use plain html inputs for the textboxes since you won't be able to get to them on the other page the same way you would if posting back on the current page. You'll have to get the posted from variables using Request.Params. You will still need to use <asp:Button.
If the other page is in the same site you would set the button postbackurl like: "~/Login.aspx" assuming that the page you are posting from is running under /ccweb/
But you could also postback to the current page and then redirect out of postback on successful login, then you can get to the values of the textboxes more easily using the server ids
string acctNo = AccNo.Text;
also posting to a different page makes it hard to handle if the login fails.
Myself if I was going to make a custom login I would not make it a control hosted by a CMS page, I would make a standalone page. You can make our Sign In link point to your custom page by adding this in user.config:
<add key="LoginPageRelativeUrl" value="/Login.aspx"/> assuming that page exists in the root of your site
Then you have full control over the page and can just postback directly to the same page like our built in login page does.
Hope that helps,