Oh great. Here we go... another installation guide to add to the pile of thousands that already exist. What makes this guide so special? Good question. Let me tell you.
This guide will NOT be instructing you on how to download and set up a "pre-installed" copy of the game. Instead I will be providing a singular link, just one, to the complete 3.0.1 installable client and every patch needed to run the game. This package was put together by me after painstakingly scouring the internet for files that aren't easy to come by anymore. Most of the sites that hosted the patches are no longer up or do not host the patches anymore. But I have found all 21 of them and an installable client and packaged them into one 7z archive. You should know that this is the enUS version of the client. It should work no matter where you are in the world, but just bare in mind this won't be any other language but US English.
Simply put, the "pre-installed" clients may work but there are several compatibility issues with many addons. This installable client doesn't have those issues (provided you are downloading the right version of the addon, ie. using a version of recount designed for 3.3.5a and not one desgined for 6.0.3). Another benefit is by installing it you are letting your system create the proper registry entries and not chewing up your PC's filing system. Simply downloading the "pre-installed" client will not create a registry entry for your "Programs and Features" list, or provide a proper uninstall executable. This method will do all of that and save you from an unnecessary and inevitable Windows reinstall.
Alright, alright. Calm down.
THIS IS IMPORTANT
When prompted to choose a directory to install to, do NOT install to the default directory. Installing it anywhere else will be fine.
The first patch is in the folder labelled "Patch_1"
The second patch is in the folder labelled "Patch_2"
All the way down to patch 21.
When you get to patches 11 and 15 you will find several files, just launch the "BNUpdate" and "Blizzard Updater" executables respectively. The other files are MPQ files containing the actual patch data. For some reason blizzard decided to separate the executable and the patch for these updates.