libsilc provides libmd5.so.0
w3c-libwww provides libmd5.so.0

Indeed, for w3c-libwww a corresponding lib exists:

$ rpmls -p w3c-libwww-5.4.1-0.4.20060206cvs.fc6.i386.rpm | grep md5
lrwxrwxrwx  /usr/lib/libmd5.so.0
-rwxr-xr-x  /usr/lib/libmd5.so.0.1.0

$ rpm -qp --provides libsilc-1.0.2-2.fc6.i386.rpm 
libaes.so.0  
libblowfish.so.0  
libcast.so.0  
libmd5.so.0  
libnone.so.0  
librc5.so.0  
librsa.so.0  
libsha1.so.0  
libsilc-1.0.so.2  
libsilcclient-1.0.so.1  
libtwofish.so.0  
libsilc = 0:1.0.2-2.fc6

So, both packages conflict in what they provide. 

Worse, libsilc provides these sonames for private plugins outside
dynamic linker's search path:

$ rpmls -p libsilc-1.0.2-2.fc6.i386.rpm | grep mod
drwxr-xr-x  /usr/lib/silc/modules
-rwxr-xr-x  /usr/lib/silc/modules/aes.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/blowfish.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/cast.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/md5.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/none.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/rc5.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/rsa.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/sha1.sim.so
-rwxr-xr-x  /usr/lib/silc/modules/twofish.sim.so