As has been previously mentioned, glDrawPixels clamps floating point values to [0, 1] even when drawing to floating point buffers (also using the NV30 emulation in the latest 42.01 driver).
As further input, glDrawPixels ignores any enabled fragment programs, which is probably the reason floating point values get clamped.
On another note, it would be really useful to have a format “GL_RG” in order to directly communicate with GL_FLOAT_RG_NV buffers in glRead/DrawPixels and glTexImage2D…
Michael