IPB Spioiler tag

I just downloaded a hack to get a spoiler tag for my IPB board. I can't make heads or tails out of this. Any idea how I can set this up on my board?

It tells you what to do there.

First open <b>/sources/lib/post_parser.php</b> and find <b>if ( $in['CODE'] == 1 ) {</b> in the file. Below that add <b>$txt = preg_replace( "#\[spoiler\](.+?)\[/spoiler\]#ies", "\$this->regex_spoiler_tag('\\1')", $txt );</b>

Etc... Just do what it says. Add after, add before, replace. Those are the basic procedures. Can't get much simpler.

I'm editing the php just like it's telling me and it's still not working, I'm even copying and pasting to see if I can get it right. Can somebody edit this for me? It's not going well for me.