This seems to be because I'm missing some UTDC dll (can't remember exactly), and when I try to install it from the prompt the game gives me, it just crashes. Can anyone point me in the right direction on this?

You can find version 1.18 here.
However, I have no idea if it's the latest (probably not} or what version the server requires.
Other versions can be found at [url]http://www.anticheat.co.uk[/url]
To install UTDC, unpack files into UT system folder.

Okay, I dumped all those 1.8 files into the system folder. Tried to get onto a server, got the same "you must install UTDC" message, clicked on install, got this message and a crash to Windows:
Failed to find function Main in BatchExportCommandlet Transient.InstallClient0.BatchExportCommandlet0
History: UObject::ProcessEvent <- (UTConsole Transient.UTConsole0, Function UTMENU.UITConsole.UWindow.KeyEvent) <- UEngine::InputEvent <- UWindowsViewport::CauseInputEvent <- WM_BUTTONUP <- UWindowsViewport::ViewportWndProc <-WWindow::StaticProc <- DispatchMessage <- 00060446 514 <- MessagePump <- MainLoop

Tried it again with 2.1 from a different site, same problem.

Just a hunch but try increasing your netspeed. You can search or post about the problem at UnrealAdmin.org.