Most Oracle stuff is free to download and use for personal use. For example, I have their database, application server and IDE installed on my work machine at home. AFAIK, JDeveloper 10g is still considered a "preview" version. Meaning, you probably don't want to write production code with it. Also, JDeveloper projects < 10G need to be "converted" upon loading into 10G. I've played around with 10G and it's pretty nice. I've been using their 903 version for about a year now and it's pretty good also.