I think you'd want something like:
Code:
<a href="{vb:raw post.field7}">{vb:raw post.field7}</a>
if you were inserting it in postbit, that is.
But if you want it to show up on the profile page, I think you want to edit template memberinfo_profilefield and check $profilefield[profilefieldid] == 7. So something like:
Code:
<vb:if condition="$profilefield[profilefieldid] == 7">
<a href="{vb:raw profilefield.value}">{vb:raw profilefield.value}</a>
<vb:else />
{vb:raw profilefield.value}
</vb:if>
(the {vb:raw profilefield.value} is a line that already exists in the template, so you want to find that line and replace it with the above.