I had to do a couple of things to get rdesktop to successfully and reliably connect with my windows 2003 servers-

On the server go to- Administrative Tools->Terminal Services Configuration. In the 'General' tab I set it at-
Security Layer-> RDP Security Layer
Encryption Level-> Client Compatible

Under the 'Logon Settings' I've set it to 'use client provided logon information' to prevent having to type the user/password twice.

On the tablet, set it to use 8bpp color depth or it'll crash on logon...

At this point it would work 'sometimes'

To get it working consistently I had to create an ssl certificate and install it, then on the same tab of the Terminal services configuration window, set terminal services to use that certificate.

That in mind, it works every time now. (I regularly connect to 5 Windows/SBS 2003 servers and 2 Windows 2000 servers this way for work...)

hope this helps,
kernelpanic

p.s.- there is something with the rdesktop maemo package where once you've crashed by not setting 8bpp, you may need to reboot the tablet to get it to successfully start.

<EDIT> I've compiled the debian etch rdesktop1.5 package for armel and installed it on my tablet. and 16bpp works. (but it's not hildonized. i.e.- once minimized you can't restore the window, hardware keys don't work so '-f' must be specified on the command line, etc...) But it looks as if most of the issues (aside from ecnryption settings) are specific to the maemo port... </EDIT>