Hardware and bandwidth requirements depend on many factors: which
OS is running on your Terminal Server, which applications your
users are running on the TS (16-bit applications are CPU killers,
graphics intensive applications like CAD programs are bandwidth
killers), how much printing is done, etc.
Minimum bandwidth for a useable RDP Session = 26.4Kbps
800×600 @16 bit color – 26.4Kbps per session
1024×768 @256 colors – 24.6Kbps per session
each increase in screen resolution or color depth requires about 3-
4 Kbps more bandwidth.
RAM for each RDP Session = 10-15 MB per user + what their
applications need (can easily get as high as 40-50 MB per user)
This is on top of the RAM that you need for the base OS.
Dual CPUs, the faster the better.
Have a look at Patrick Rousse’s hardware recommendations: