Sorry Yanto, haven't signed into skype in quite a while. Server 2003 sp2 is absolutely supported by avast 4 server, as I have a few running it. I also have SBS 2008, server 2008, and now I'm about to have SBS 2011 with it (haven't tried it yet though, but it's just 2008 server core so it should work just fine except for the exchange 2010 part).
As for the interface not showing up, it could be a setting in the computer catalog. You can prevent users from seeing the "skinned" version of avast by using policies on the computer group.
As to why you can't see the interface, that doesn't seem right. I'd remove the client and reinstall if possible. I know that this is a server machine so it can be difficult to do much work as they're usually in use a lot of the time. Try to do it during off-hours if needed.
All that I can say is that I completely confirm that avast 4 server works just fine on server 2003, especially since that's running on XP kernels, which we all know works just fine.
Now that I've posted in this thread, it will remind me when you post something in here and I don't have to rely on skype, so I should be on top of it.
Let me know what you find out after the re-install.