If using OSX 10.4, you are limited to LW 4. You have choice of LW 4.18 or below. I normally recommend LW 4.16 but that's up to you. LW 5 requires Java 1.6 which is limited to (1) OSX 10.5, and (2) a reasonably new intel machine (within last 2-3 years depending whether it's a macpro or imac or macbook.)

To get LW 4.16 see Downgrading to LimeWire 4 from 5 & resuming incomplete downloads. Just discovered LW have stopped supplying an old versions page.