just to expand on what Colourless said on jitter control.
all D3D display registry settings are under
\HKEY_LOCAL_MACHINE\System\CurrentControlSet\Services\Class\Display\<adapter_number>\D3D
(for win98, that is) and 2x fsaa control is as follows:
SSTH3_PRIBUFVTXOFFX_2SMPL -- for controlling the 1st sub-sample offset along the x-axis
SSTH3_PRIBUFVTXOFFY_2SMPL -- for controlling the 1st sub-sample offset along the y-axis
SSTH3_SECBUFVTXOFFX_2SMPL -- for controllig the 2nd sub-sample offset along the x-axis
SSTH3_SECBUFVTXOFFY_2SMPL -- for controlling the 2nd sub-smaple offset along the y-axis
above entries are all of string type, and take arguments of the form "<integer_part>.<fractional_part>" which control the x- or y-axis offset (i.e. 'jitter') of the respective sub-sample in respect to the macro-sample center. the valid randge for an offset covers at least the [-3.0, 3.0] interval, with effective graularity of 1/16 (i.e. 0.0625). the magnitude of the values passed corresponds to a factor of a pixel unit, i.e a value of 1.0 denotes an offset by one unit along the respective axis.
hope the above is of any help