EDIT
I wrote a quick way to get multi-core: http://charlesleifer.com/blog/solr-ubuntu-revisited/
Following the instructions of the two sites below, I installed Tomcat 6 and Solr 1.4.
I successfully launched it and launched it on a server with 9.04 with multi-core support, but in 10.04 I cannot get it to work.
I can contact localhost: xxxx / solr / in field 10.04 and see the only link to Solr Admin, but after the link I will go to page 404 with the following output:
/solr/admin/
HTTP Status 404 - missing core name in path
The requested resource (missing core name in path) is not available
/solr/site 1/, - 404.
<cores adminPath="/admin/cores">
<core name="site1" instanceDir="site1" />
<core name="site2" instanceDir="site2" />
</cores>
<Context docBase="/var/solr/solr.war" debug="0" privileged="true" allowLinking="true" crossContext="true">
<Environment name="solr/home" type="java.lang.String" value="/var/solr" override="true" />
</Context>