MultiCoin is AFAIK the only GUI client that supports NameCoin. Is there a trusted Windows binary to be found?
I have been doing windows builds of multicoin-exp, but have not heard of anyone using them so don't keep it up to date unless I get a request usually.
http://www.wuala.com/jbw9/pub/Bitcoin/multicoin/MultiCoin-exp/src/bitcoin.exe/ is actually mutlicoin, however I am pretty sure this version only works with the config file that would have been compatible with .62 and needs to be updated for .63 now that we have passed block 19200. I can update it if anyone wants it to be.