Using the XML modules I just downloaded from the beta update center 
(200111301106 build), if I try and open a tree (or expand it in the explorer 
window) for my existing EJB deployment descriptors, I just get a "Parse fatal 
error..." message.  However, if use the Check XML/Validate XML menu options on 
them, there are no errors displayed (and they deploy okay, so I believe they're 
correct).

The problem appears to be to do with the
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 
1.1//EN" "http://java.sun.com/j2ee/dtds/ejb-jar_1_1.dtd">
line - this is identical to the example in the EJB 1.1 spec.  Likewise, the EJB 
2.0 spec says
'All valid ejb-jar deployment descriptors must contain the following DOCTYPE 
declaration:
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise
JavaBeans 2.0//EN" "http://java.sun.com/dtd/ejb-jar_2_0.dtd">'

If I create a new xml file named ejb-jar using the "XML with DTD" template, 
open it up in tree view and change the public ID on the main node to either of 
the above (or any of the separate strings, with or without quotes), I get 
an "Invalid public ID" warning dialog, and it reverts to <DEFAULT>.  Whether or 
not it really is invalid, I wouldn't know.  However, since there's likely to be 
a lot of files with these DOCTYPE declarations, I think the XML module ought to 
be able to handle them.