Apache Solr runs of Java 6 or greater. When using Java 7, be sure to install at least Update 1! With all Java versions it is strongly recommended to not use experimental
-XX JVM options. It is also recommended to always use the latest update version of your Java VM, because bugs may affect Solr. An overview of known JVM bugs can be found on http://wiki.apache.org/lucene-java/SunJavaBugs.
CPU, disk and memory requirements are based on the many choices made in implementing Solr (document size, number of documents, and number of hits retrieved to name a few). The benchmarks page has some information related to performance on particular platforms.