I tried out the freebie version of PocketCloud from Wyse for RDP to a Windows Vista machine.
Worked well enough over wifi, it offers different resolutions, and I was using one much higher than my Streak's but it let me drag the screen position around easily enough to show the bits I wanted when I wanted.
You can bring up / put away the Streak's soft keyboard as desired, taps on the screen were sufficient to act as mouse clicks to open/close apps, position on fields for data entry, etc.
If you were intending to use it over something other than wifi, no idea how well that would work (due to performance) or how quickly you'd bump into data limits, but as a technology for use in a pinch, it's quite OK and feasible. Not really suited for long term use though, I think for that you'd want a bigger tablet or a netbook at minimum.