TheFakeSheikh's advice is mostly there. Specifically what you need to do is find the Receipts folder & remove the install limewire.pkg file, before the system will allow you to install an earlier version. Receipts folder sample image

We'd actually recommend you install LW 4.16 rather than 4.18 but that's up to you. http://www.gnutellaforums.com/downlo...downloads.html but you only need to see step 1. Steps 2 & 3 are only if you actually used LW 5 & wanted to move back to LW 4.