AFAIK, The GB pound sign is not an ASCII character. you'll have to use wchar and unicode to get it to output in the Windows console.
this outputs all ASCII and extended-ASCII characters to the console in W2K, and £ isn't there on mine:
for(unsigned char i(0); i!=16; ++i)
for(unsigned char j(0); j!=16; ++j)
std::cout << static_cast<char>(i*16 + j) << " ";
std::cout << std::endl;
Edit : as for actually using isalpha, isalnum, etc with a wide char, I don't think it's possible, there might be a wide char version available in some 3rd party library, but I couldn't turn anything up in google.