What is GUIMiner?
GUIMiner is a graphical frontend for mining Bitcoins, providing a convenient way to operate Bitcoin miners from a graphical interface. It supports both AMD and NVIDIA GPUs, as well as CPU mining. You can choose between pooled mining and solo mining - the software embeds a list of mining pools to choose from.
Where can I download GUIMiner?
You can download GUIMiner from the official GitHub repo.
Can I use GUIMiner to mine Litecoin?
In order to mine Litecoin, you have to use GUIMiner-scrypt.
Where can I get news and updates about GUIMiner?
Have a look at the official forum thread on BitcoinTalk.