this may help:
there should also be a certification matrix for soa suite if you check the downloads page (somewhere)
I have been able to successfully install Jdev/SOA 11.113 -11.115 against xe 10 on linux and windows.
Edited by: jo**** on Dec 26, 2011 9:02 AM
Download the XE latest and install SOA Suite 11g version, before that check with the above url for the version compatibility and start Njoying SOA experience.
You can download from the below URLs