Voxengo's PowerShaper is a free VST based overdrive/distortion plug-in. I no longer have this plug-in as I've switched from Cubase SX on a PC (where I was running this) to Pro Tools LE on a Mac, and this plug-in is only PC and VST compatible. Since it was a number of years ago that I ran this plug-in, I can't remember the installation process exactly. However, I can't see a reason why anyone should have a problem downloading and installing this plug-in as long as you have the proper configuration to run it. The interface of the plug-in is incredibly simple, consisting of parameters just for input gain, intensity, and output gain. That's all that there is to it, so a manual isn't something that is necessary with this plug-in.
When I had this plug-in, I was running it in Cubase SX on a Hewlett Packard Pavilion dv8000 notebook with a 3.0 Ghz processor and 2 GB of RAM. I don't ever remember having an issue with the Voxengo PowerShaper, but I honestly never had a need to run more than one of these within a session. I'm not a big fan of this plug-in, so while I did keep it in my arsenal for as long as I had a PC running Cubase, it didn't see much action. That having been said, it is easy to tell that this doesn't take up much processing power, so I'd imagine that most users will be able to run this without performance problems.
While it's hard for me to speak negatively of a free plug-in, the Voxengo PowerShaper isn't a plug-in that I can really recommend. In general I'm not a big fan of software overdrives, but I will admit that they have come a long way in recent years. However, being that the PowerShaper has been around for a while, it still has a rather stale and unrealistic sound in my opinion. Being that it is indeed free, there isn't any harm in downloading it and trying it for yourself, but if you want some decent sounding overdrive in plug-in form, you're going to have to go with something a bit newer.