I was able to get things working my using the instructions in http://support.microsoft.com/kb/288367/ to run Excel as a specific user through the DCOM interface (not the default "System" user) for several systems, but on one system, whenever I configure the DCOM interface (using DCOMCNFG) to run Excel as a user I get errors whenever I start Excel interactively (e.g. "Cannot use object linking and embedding") and JExcel doesn't work.  The errors go away if I set the Identity tab in DCOMCNFG to "Launching User" (but then my application doesn't work).

Any  ideas on security settings that I can change, etc....?