It might be possible, although I doubt the Struts folks intended for
anyone to do that. AIUI, Struts 2 is designed to work with the JSTL
(JSP Standard Tag Library), which took over a lot of the functionality
originally only available from Struts 1 tags.
I have worked on several Struts 1 projects, but I only know about
Struts 2 what I've read in their API and taglib docs. That does reveal
that they've dropped a lot of the redundancy between their stuff and
the JSTL.
Having used both, I can't see any reason why you couldn't use them in
the same project provided you gave them different URL suffixes to work
with (eg. struts1 with .do and struts2 with .action, or similar). The
two frameworks are essentially independant: struts 2 contains almost
nothing of the original struts, instead building on the WebWork
framework. Even the config files have different names under struts2,
not to mention different auto-discovery mechanisms.
I've never actually tried it, though, so your mileage probably will
vary. The best advice I can offer is to "try it and see".
-o