There are two main memcached clients for PHP, memcache and memcached. You can see a comparison of the two versions here. The biggest difference is probably the memcached extension's reliance on libmemcached. This gives the memcached client a number of additional capabilities. In my searching though, I have been unable to find a working dll for the memcached client library. This means that the memcache library is basically your only choice on Windows unless you want to try and compile it yourself (based on the lack of an available dll this is probably very difficult) or use a pure-PHP library like xslib-memcached, but you're likely to find much more support for the memcache client.
I have not attempted to use the memcache client on IIS, but I have used it with Apache on Windows 7 (32-bit builds on both 32-bit and 64-bit Windows) connecting to a local memcached server, so I know that there are working builds of this client.
If your running on AWS, you should really consider using Linux. It's much cheaper than running Windows instances and will probably run PHP better than IIS on Windows.