To use temporalsoften as smoother (using Soulhunter's parameters):
UnSmooth(smoother="Temporalsoften", params="2,3,3,mode=2,scenechange=10")
To use simple blur as smoother (resulting effect is unsharp mask sharpening):
UnSmooth(smoother="Blur", params="1.0")
That should pretty much explain it. Strings need to be wrapped in Chr(34)s instead of quotes, because of AVISynth's undocumented inability to use TEX-Style quotes.
Example:
UnSmooth(smoother="Subtitle", params=Chr(34)+"This will give a funky effect"+Chr(34)+", font_color=$FF0000")
As you can see the Chr() and strings are chained together using math operators.