If you are compiling 0.5.4 with gcc-3.2, you will need to add the following to src/HostCacheConnection.cpp:
#include <iostream>

On the other hand, src/SHA1Storage.cpp fails to compile with:
SHA1Storage.cpp: In member function `QString* SHA1Storage::get(SharedFile*)':
SHA1Storage.cpp:103: no method `std::char_traits<char>::eos'

This is a problem because of the imgration from strstream to stringstream. I don't have a solution yet, though :-(