You're gonna have to download the cvs of the gtk2 version.
cvs -d:pserver:firstname.lastname@example.org:/cvsroot/sylpheed-claws login
press enter when the login prompt comes up.
cvs -z3 -d:pserver:email@example.com:/cvsroot/sylpheed-claws co -r gtk2 sylpheed-claws
Now go into the sylpheed-claws directory and type './autogen.sh'
If it doesn't find all the libs then you can either disable the dependent plugin / feature, or you can install the libs and rerun ./configure.
When that's all done type 'make', then su into root, and then a 'make install' should get it there for ya.