I'm not sure whether it's appropriate, but with Rtools 2.15 and R 2.15.1
under windows, I had to kick off my package with
...
R = new RInside(argc, argv, true);
R->parseEval("library(\"methods\")");
(*R)["xyz"] = LOAD_RCPP_MODULE(xyz) ;
...
Didnt have time to investigate further, sorry
P