slow connection from xp viewer to mac os x

[info]

We're using RealVNC Viewer version 3.3 on Windows XP and connecting to a Mac
with OS X using Remote Desktop version 3.

The connection is made and keeps, but the connection is very slow with
tremendous lags per key stroke. We've tried the current version of viewer
but have more success with the older version.

What would the optimum settings be for either version 3.3 or 4.1.2 and would
there be any other settings for the Mac remote desktop that we would need?