I tried this today, too. And cannot replicate the issue - I installed JBDS 7.1.0 w/ EAP in Windows 7 32bit using Oracle JDK 1.7 Update 51. The issue that Sebastian is facing would manifest itself by popping up the Installer Error window - it doesn't happen in my case. Unfortunately I don't have any Vista installation available to try it there.
I tested on Windows Vista Home Edition with latest updates and the same JVM, but still could not replicate it. For some reason p2 director decides to use packed artifacts and the only way to find out why is dig into p2 source code.
FYI, the three issues above are now tracked in JIRA:
Nick, I can take care of JBDS-2880, could you do the same for other two?
Thanks a lot! Please let us know how it's going on.
By the way: I didn't have any trouble installing on Windows 7 at home.