It looks like the R 2.12.0 binary has been released for windows. I've made some quick adjustments such that it should be possible to download a binary build of OpenMx for 32-bit windows with R 2.12.0. Our team is working on the 64-bit windows, this will be very cool when cross-compilation is working. We need to compile libnpsol for 64-bit windows so have patience.
We will be phasing out the binary releases for R 2.9.x. See this discussion  for why, there are currently 9 compilations requested for a binary release, that number is not going to 12. This means that R documentation (question-mark support) will no longer work on R 2.9.x and earlier. If this is a problem, you can either upgrade your version of R or build OpenMx for your platform.