If you are like me and have an old computer that doesn't support SSE3 but still want to use this, I figured how to do it with the help of Rollyco and will explain it here.
Before I explain how, you need to keep in mind it's going to take a loooong time to encode on an old computer. With my Athlon 2800+ single-core with only SSE, it takes about 71 hours to encode 1h33 of video. Now, if your crazy like me and still want to do it because of the amazing quality it produce, here's how you do it:
1. Download MeguIV, copy it to the folder of your choice and start it(it will create a folder named sandbox, this is normal).
2. There are 3 plugins that are causing problem: RemoveGrainSSE3.dll, RepairSSE3.dll and nnedi2.dll.
The current NNEDI2 may work for your computer. It's probably the people with only SSE that need the new one so you could try only replacing the first 2 and see if it works.
To download the correct versions, go to the avisynth wiki(google it, it's easy to find) and search for RemoveGrain(Repair is included with RemoveGrain) and download the version 1.0b.
For nnedi2, download this version from the Doom9 forum
NNEDI2.dll .
3. Extract the RemoveGrain and Repair dll compatible with your computer(if you don't know what SSE version your CPU can handle, download CPU-Z and check in the instructions section) and rename them to RemoveGrainSSE3.dll and RepairSSE3.dll.
4. In MeguIV, click on Options, settings. Go to the "Program Paths" tab and click on the ... at the right(it doesn't matter for which program it is).
Go to your windows partition(probably C
and into the MeguIV, Avisynth 2.5, plugins folders. In the filename box, erase what's there and write * and press enter(this will show all the files in the folder).
Now copy the 3 files you just downloaded and paste them in the plugins folder of the open file window(you need to do it like this because it's a virtual folder). It will ask if you want to overwrite the existing files and click yes. Press cancel to close the open file window, exit the settings page and it's all done.
You should now be able to use it. Just follow the tutorial in the first post and you will be able to produce video of amazing quality.