Ok, I'm hoping someone will be able to help out with this...
I've taken a look at Altova's StyleVision (found at
http://www.altova.com/solutions/xslt-tools.html, I'm using a 30-day trial) to see if I might be able to use that to design this sheet. I set it up so that the Schema it points to is C:\Program Data\Hero Lab\data\savage\docs\customoutput.dtd which works great and show up all the stuff in the little Schema tree it provides. I then set the "Workng XML" file to C:\Program Data\Hero Lab\customoutput\fullsheet_savage\output.xml, which give me an error about there not be a declaration in element "document" for attribute "signature". And finally I set the XSLT file to C:\Program Data\Hero Lab\customoutput\fullsheet_savage\statblock.xsl. I get no errors there, but it also doesn't show that layout on the Design pane, either. (EDIT: turns out it isn't able to use an existing xslt file to show you the output, only the one in it's format.)
Anyone have a good idea on how I should be laying out files in a tool like this to work correctly? It seem like I've got the dtd file right, but maybe not the other ones? I'd definitely appreciate it if anyone has any experience doing this kind of thing and hopefully I can put together a sheet or two that might be halfway decent for folks before my trial expires (sorry, I don't intend to spend $130 for the product just for this one purpose.)