Compiling RCurl from source on Windows
Looks like the RCurl v1.95-4.3 binary file for Windows has been uploaded to CRAN as of this morning. I was dealing with the exact same issue as you, and after building the binary file from source, all was well with my usage of RCurl again!
http://cran.r-project.org/web/packages/RCurl/index.html
install.packages("RCurl_1.95-4.3.zip", repos=NULL, type="source")
Not sure which version of cURL you have on your machine, but as it states on this website that version 7.37.0 seems to work for Windows 8
EDITYou can try this manual download. It specifies the .dll files you mentioned and is compatible with 64 bithttp://www.stats.ox.ac.uk/pub/RWin/bin/windows/contrib/2.15/