You know that this topic is two years old? You found only this one when performing your search? I'm sure there are more recent topics about the same subject.
You shouldn't follow or use files from old tutorials.
About your question, you didn't provide a lot of information.
I think what you want is to install the USBLoaderGX forwarder.dol into Priiloader? (don't use
Preloader, now there is
Priiloader).
You have to place your .dol on the root of the SD card.
Don't use the forwarder.dol from this topic, instead download and use the forwarder3.0.dol from the
latest version.
If you had read page 2 of this same topic, you would have found the
step by step guide to do it.
You need to do this installation step only one time, you don't need to keep the forwarder.dol on your SD card once it's installed in the Wii.
There is another way to boot straight in USBloaderGX, but it requires Bootmii installed as Boot2, a
modified bootmii file, and the
UNEO forwarder channel installed.
Next time, please don't bump a too old topic, and don't follow outdated guide, it could brick your Wii by providing incompatible files for newer consoles.
If you still have a problem on how to install Priiloader or use USBloaderGX, you should create a new topic in the Wii - backup loader forum.