Thanks. I have sort of fixed the problem. It must have been a Java installation program, because I had to uninstall the JRE and then reinstall a Java package from the following repository (BTW, I am running Ubuntu(debian)):

deb http://ubuntu.tower-net.de/ubuntu/ warty java

I also had to enable the multiverse packages:

deb http://archive.ubuntu.com/ubuntu/ warty multiverse

...so that I could download another package with debian-specific stuff in it. Anyway, Java works now, and LimeWire recognises it, but now I am getting another error when I try to start LimeWire:

LimeWire version 4.8.1
Java version 1.5.0_01 from Sun Microsystems Inc.
Linux v. 2.6.8.1-3-386 on i386
Free/total memory: 1127408/2031616

com.limegroup.gnutella.gui.GUILoader$StartupFailed Exception: invalid update.ver
at com.limegroup.gnutella.gui.GUILoader.sanityCheck(G UILoader.java:277)
at com.limegroup.gnutella.gui.GUILoader.load(GUILoade r.java:43)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Nativ e Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Native MethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(De legatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at com.limegroup.gnutella.gui.Main.main(Main.java:31)

STARTUP ERROR!




FILES IN CURRENT DIRECTORY:
/usr/lib/LimeWire/LimeWire.jar
LAST MODIFIED: 1110397789000
SIZE: 5264661

/usr/lib/LimeWire/COPYING
LAST MODIFIED: 1110397789000
SIZE: 18349

/usr/lib/LimeWire/MessagesBundle.properties
LAST MODIFIED: 1110397789000
SIZE: 99605

/usr/lib/LimeWire/Limewire.desktop
LAST MODIFIED: 1110397789000
SIZE: 234

/usr/lib/LimeWire/Limewire.mandrake
LAST MODIFIED: 1110397789000
SIZE: 164

/usr/lib/LimeWire/commons-httpclient.jar
LAST MODIFIED: 1110397789000
SIZE: 463786

/usr/lib/LimeWire/MessagesBundles.jar
LAST MODIFIED: 1110397789000
SIZE: 2057649

/usr/lib/LimeWire/ProgressTabs.jar
LAST MODIFIED: 1110397789000
SIZE: 5964

/usr/lib/LimeWire/README.txt
LAST MODIFIED: 1110397789000
SIZE: 828

/usr/lib/LimeWire/SOURCE
LAST MODIFIED: 1110397789000
SIZE: 268

/usr/lib/LimeWire/clink.jar
LAST MODIFIED: 1110397789000
SIZE: 627752

/usr/lib/LimeWire/runLime.sh
LAST MODIFIED: 1110397789000
SIZE: 2612

/usr/lib/LimeWire/root
LAST MODIFIED: 1116490075000
SIZE: 4096

/usr/lib/LimeWire/commons-logging.jar
LAST MODIFIED: 1110397789000
SIZE: 59154

/usr/lib/LimeWire/daap.jar
LAST MODIFIED: 1110397789000
SIZE: 310773

/usr/lib/LimeWire/data.ser
LAST MODIFIED: 1110397789000
SIZE: 358

/usr/lib/LimeWire/hashes
LAST MODIFIED: 1110397789000
SIZE: 298

/usr/lib/LimeWire/i18n.jar
LAST MODIFIED: 1110397789000
SIZE: 25678

/usr/lib/LimeWire/icu4j.jar
LAST MODIFIED: 1110397789000
SIZE: 741440

/usr/lib/LimeWire/id3v2.jar
LAST MODIFIED: 1110397789000
SIZE: 94430

/usr/lib/LimeWire/jcraft.jar
LAST MODIFIED: 1110397789000
SIZE: 135834

/usr/lib/LimeWire/jdic.jar
LAST MODIFIED: 1110397789000
SIZE: 70800

/usr/lib/LimeWire/jl011.jar
LAST MODIFIED: 1110397789000
SIZE: 255016

/usr/lib/LimeWire/jmdns.jar
LAST MODIFIED: 1110397789000
SIZE: 69306

/usr/lib/LimeWire/libIdleTime.so
LAST MODIFIED: 1110397790000
SIZE: 4020

/usr/lib/LimeWire/libtray.so
LAST MODIFIED: 1110397790000
SIZE: 12084

/usr/lib/LimeWire/limewire-16.png
LAST MODIFIED: 1110397789000
SIZE: 747

/usr/lib/LimeWire/limewire-32.png
LAST MODIFIED: 1110397789000
SIZE: 775

/usr/lib/LimeWire/limewire-48.png
LAST MODIFIED: 1110397789000
SIZE: 3157

/usr/lib/LimeWire/logicrypto.jar
LAST MODIFIED: 1110397789000
SIZE: 227510

/usr/lib/LimeWire/looks.jar
LAST MODIFIED: 1110397789000
SIZE: 630634

/usr/lib/LimeWire/mp3sp14.jar
LAST MODIFIED: 1110397789000
SIZE: 40064

/usr/lib/LimeWire/spacer.gif
LAST MODIFIED: 1110397789000
SIZE: 49

/usr/lib/LimeWire/themes.jar
LAST MODIFIED: 1115970814000
SIZE: 77312

This is so confusing! Help!