As promised, here's the rundown on why you won't be using RDP to connect Linux machines to Windows NT Server 4.0, Terminal Server Edition (TSE) or Windows 2000 Server Terminal Services any time soon. First, the interface you use to set up the Linux RDP client is incredibly cumbersome. It's difficult to set up the connection, a problem that isn't restricted to the RDP client—both Linux-based Windows terminals I've used have had poorly designed interfaces. In addition, the way that the network and connection configuration information is arranged makes it difficult to tell what's wrong when you've set up the connection improperly and difficult to fix problems when you isolate them. Although the error messages you get from the native Windows RDP client aren't great, they at least tell you something (e.g., that the client can't find the server you're trying to connect to or that the server has refused the connection). And, as I noted a couple of weeks ago, the error messages that you get from HOB's Java-based RDP client are somewhat more helpful than those you get from the native Windows RDP client. The Linux RDP client, however, offers no error messages and no online help. If you have experience setting up Windows terminals (and are therefore more prepared to troubleshoot them), this might be little more than an annoyance; otherwise, the lack of feedback can be a real problem.
Second, the RDP client I've seen has a security hole you could throw a dog through. To successfully connect to a TSE server, you must supply a username and password with each connection. You don’t have the option of logging on to the terminal separately, after initiating the connection to the server. If you don't supply the password, the connection will fail. (I discovered this security hole by trial and error. There's no warning message that prompts you to provide a password to make the connection.)
Third, once you get into the RDP session, it's disappointing. The connection works, but it doesn't perform as well as a native Windows RDP session. The display updates are slow, and I ran into some graphical output problems (e.g., blocks of text displayed as black blocks at one point, although the problem disappeared when I terminated the session and then reconnected). The Linux RDP client is just not as comfortable to use as either the ICA client for Linux or the RDP client for Windows.
Fourth, although the protocol exists, it's not widely available. RDP ships with two Linux terminals (Boca Research's BocaVision JNC205 and Brace's Thinworks e3000), but other Linux terminals and IBM's thin clients offer only ICA for connecting to Windows terminals. When you consider Linux RDP’s other issues, it's not surprising that no other vendors are including it in their current Linux Windows terminals. And after weeks of searching Linux sites and bugging any Linux-savvy associates I could corner, I haven’t been able to find a copy of the client available for download.
The bottom line? The Linux-compatible RDP client just doesn't work. It's not that it can't work, or that it's incapable of working—it simply doesn't work well now. If you need to connect to Windows applications from Linux now, you're better off with another option, such as Citrix's ICA client or GraphOn's WinBridges. At this point, Linux support for RDP is more a theoretical solution than a practical one.