Let's clarify something:
An <a> by itself can not post. However, an <a> associated with a form can most certainly post. Take this example:
<form action="postDestinationPage.aspx" method="post" name="myPostForm">
<input type="hidden" name="hidSomeHiddenValue" value="12345">
:document.myPostForm.submit();">Cl ick Me</a>
Are you looking to create isolated hyperlinks that post to pages outside of your .net web application or are you just interested in having a link act as a button on a .net web form? If the latter is the case, then you can use the LinkButton control. This results in behavior identical to a regular button but with a hyperlink instead.
Work smarter, not harder