[gh0sth@cker]

When you download the crack it will usually be in the form of a RAR, ACE or ZIP file. These are methods of compression, and you should download WinRAR, or WinACE to open them.
You will probably find an exe in this. Copy and paste the new exe to the folder where the game is installed. It will ask you are you sure you want to overwrite the original file. (btw - it is a good idea to beforehand, locate the original exe and add .bak to the end of it's filename just so you can easily get it again if need be).
This is the simpliest form of a no-cd crack where the game just has a cd-check and all the data is already present on the hard drive.

If however the installation didn't copy all the data to the hard drive, then you may find instructions provided within the file you downloaded as to what to do next. You may need to copy some of the data on the cd to your hard drive and/or apply a patch.

There will usually be instructions contained within the RAR file listing what needs to be done. Sometimes it is in the form of a txt file which will open fine, but it may also be an .nfo file which can also be easily opened with notepad.