After all these years, there is still a lot of confusion about Personal Edition and Express Edition capabilities.
First of all, the Personal Edition (PE), Enterprise Edition (EE), Standard Edition (SE) and Standard Edition One (SE-1) are all found in the same download. The choice of Edition is made at install time, not download time. Fire up the installer and the Edition will be available either in a drop-down menu or in a radio-button list. (On the other hand, Express Edition, or XE, is a separate download from http://download.oracle.com)
Second, there is no difference in the installed software between SE and SE-1, so the same selection is used for either one. The difference is in the license agreement as paraphrased on page 12 of the Software Investment Guide at http://www.oracle.com/corporate/pricing/sig.html
When to choose PE or XE?
Personal Edition is *the most powerful version* for the price. It is a single user license of the Enterprise Edition with nearly all options and features turned on. It is designed for Developers who need access to Oracle Support.
Express Edition is the smallest version. It is light weight (under 300M download instead of 1-2GB download) and has the same SQL and PL/SQL engine as the Enteprise Edition, BUT it does not include Java in the database so advanced things like Java Stored Procedures and related Oracle-supplied functionality are not possible. It also has limits in how much data may be stored (4GB). That means it can only store about 20 years of accounting data for a typical under-25 person company.
Express Edition is IDEAL for a beginner to get used to developing using an Oracle database. However, one can NOT learn to administer an Oracle DB on Express Edition and therefore it is useless for a person who wishes to learn how to be a DBA.
Personal Edition also does not permit Management Packs to be licensed. Therefore performance tuning, diagnostics, etc. are not technically available. For DBA practice, Personal Edition is also not ideal - one really should install the Enterprise Edition to learn about those tools.
I really wish Oracle would rename Personal Edition to Developer Edition
... and make it available on Linux as well.