Hi Mike,
Yes you can do those customizations by simply editing login.aspx.
Open it with a text editor and find these lines starting at line 16.
You can do the highlighted changes like this:
<tr>
<td colspan="2">
<img src="mylogo.png">
<table border="0" cellpadding="5" cellspacing="0" style="width: 280px;">
<tr>
<td style="text-align: center"><img style="border: none; width: 48px; height: 48px" src="<%=LoginImageUrl%>" alt="" /></td>
<td>Welcome to My Company<br /><%=Language.GetEntry("501")%></td>
</tr>
</table>
</td>
</tr>
You can put mylogo.png in the same folder as login.aspx
In future versions, we plan to allow adding logos from administration page via UI.