UkChris things can't be too bad if you can reach the test page successfully. It probably means LW is only partially blocked if at all.

Which version of LW did you install? the international or english installer? The international forces LW to use Java 1.3

I'd suggest you double-check your modem's port forwarding. If the ip was dynamic at that time then the port forwarding may have been in vain. Also make sure you save all settings. With some modems you need to re-boot the modem/router after these types of changes. I don't know if that applies to your brand or not.

I suppose you could always try updating to Java 1.5 (take the JRE)

If things still don't work, try an earlier version of LW: http://www9.limewire.com:82/download/