At my work we use Lotus Notes 6.5 for our email, meeting scheduling and instant messaging. I can't stand the horrible UI, buggy meeting scheduling and overall '90s feel when using it and would love to replace it with open-source alternatives.

So far I've been able to setup Thunderbird for email, and I should also be able to configure pidgin to do IM, but I can't find any replacement for the meeting scheduling. I need to be able to receive meeting requests and respond to them.

I've looked around trying to get the Thunderbird plugin Lightning to manage the scheduling, but everything I've read so far requires me to export .ics files from Lotus Notes or otherwise keep Lotus Notes around for day-to-day activities.

I've also looked into using Evolution as the client, but I found even less information for it than I did for Thunderbird.

How can I easily send, receive and respond to Lotus Notes meetings using an open-source alternative?

Alternatively, if there exists a full drop-in replacement to Lotus Notes I would also consider it.

Note: My desktop at work is a Windows XP machine, though I wouldn't be opposed to a solution requiring cygwin at this point.

Edit: I have no power over the server. I only want a compatible client.