It's hard to know without seeing the source code, but I would guess you can modify the css for the class .bigusername:
Code:
.bigusername { font-size: 14pt; }
to
Code:
.bigusername { font-size: 14pt; text-decoration: none;}
That will remove the underline anywhere the class .bigusername is used. If that doesn't work, you may need to add a new class there ".bigusername a" with that style info.
You can also add "none" under the text decoration part of the Main CSS for just alt2 and that may work also.