This should work?
Code:
<div align="center">
My Social Networks:<br /><br />
<vb:if condition="is_member_of($post, 2, 6, 7, 9)">
<vb:if condition="$post['field5']">
<a href="https://twitter.com/$post[field5]" target="_blank">
<img alt="Twitter" border="0" src="$stylevar[imgdir_misc]/twitter.png"/></a></if>
<vb:if condition="$post['field6']">
<a href="https://twitter.com/$post[field6]" target="_blank">
<img alt="Twitter" border="0" src="$stylevar[imgdir_misc]/facebook.png"/></a></if>
<vb:if condition="$post['field7']">
<a href="https://twitter.com/$post[field7]" target="_blank">
<img alt="Twitter" border="0" src="$stylevar[imgdir_misc]/myspace.png"/></a></if>
</div>
</vb:if>