Not home.tpl, but head.tpl
For instance replace
{if $usertype eq "C"}
{include file="customer/top_menu.tpl"}
{/if}
with
and insert one more table at the end head.tpl:
{if $usertype eq "C"}
<table width="100%"><tr><td>{include file="customer/top_menu.tpl"}
</td></tr></table>
{/if}
what concerns the second part of your question I can't catch the point.
If you want to have equal spaces between speedbar links you need to divide page width (or 100% if it isn't fixed) by total numer of links to get the one item width.
You may need
http://smarty.net/manual/en/language.function.math.php for reference