How do I use HJSplit?
ANSWER:
Download it here. Once you've done that, open it, & MAKE SURE THE FILES YOU DOWNLOADED ARE NAMED THE SAME & PLACED IN THE SAME FOLDER!
For example - Silence 18-20.rmvb.001
Silence 18-20.rmvb.002
Silence 18-20.rmvb.003
Silence 18-20.rmvb.004

Once you have accomplished that, click on JOIN & open the Silence 18-20.001.rmvb or the FIRST file, and click START because once you have all the files named the same consistently in the same folder, it'll join the files together.