Maybe you have to set the path to external application in guiminer? Is there a command line miner exist called CUDA miner? Or is it inbuilt to the guiminer?
Hm that seems like it'd be an odd requirement to not be mentioned in the program itself doesn't it? The CUDA miner option is built in to the interface of guiminer, it's legitimately under File, New Miner.
the guiminer only come with poclbm, it is like a command line invoker. it knows the command line for other miners, but to use them , you have to download them yourself.
the default path is \guiminer\miners\puddinpop\rpcminer-cuda.exe. you have to look for rpcminer cuda on the internet yourself.