You can do a few things with that. The first is make that column wider. The second is limit the amount of characters the user can use for the name. The third is to make the size of the font smaller.
For the column width you can change the "175" below to suit your needs. Keep in mind that if your user decides an extremely long name you will have to keep adjusting it.
Code:
<td class="alt2" width="175" rowspan="2"
style="border:0px" align="center">
The second option, I believe, can be defined in the admincp options.
The third would be the hardest to accomplish and not necessarily the greatest idea. You would have to alter this line.
Code:
<a class="bigusername" href="member.php?$session[sessionurl]u=$post[userid]">$post[musername]</a>