There are two versions of EclipseFP. Version 1 is fairly old and no longer actively developed. Version 2 is still under heavy development, but is the version recommended for end use.
Please note that this software is in an early development stage (alpha).
You need a Java 5.0 compliant virtual machine (JDK or JRE) installed on your system. (For Linux, Solaris and Windows systems you can find one at http://java.sun.com/).
You need Eclipse 3.1.x. If you need an older version of Eclipse, you should stick to version 0.6 of the Haskell plugins. If you don't have Eclipse, download it from http://eclipse.org/downloads/. Look for the platform runtime binaries, if you don't want to download the entire SDK. (The platform runtime contains the basic Eclipse IDE without Java and Plugin development tools.)
You need a GHC installed on your system. See http://haskell.org/ghc/ for more information and for downloads.
Download and installation is done via the built-in Update Manager in Eclipse. You can find installation instructions here.