FYI: I have reason to believe that the new transmission coming out in the 2004+ E46s is a modified Getrag Type D transmission you'll find in the current M3. It can then be changed to the SSG/SMG configuration, which explains their decision to go with Getrag for future marketing.
I personally enjoy the crisp, smooth feeling of ZF gearboxes. If you have driven both, you'll know what I mean. So, I have been tracking down information about the 6-speed in the new Z4 roadster, since it already bolts up to the M54 motors.
Since November, I have been speaking with ZF, Getrag, BMWNA, and BMWAG engineers about retrofitting a 6-speed transmission into manual 325/330s. It is coming along very nicely, and I will likely be able to offer the kit for around $3,000 including an entire brand new transmission. No conversions, all bolt up. I am still working out the details, so give me some time.
Also, I will probably work out a deal where additional optional items will include a Short Shifter, alternate rear final drive gears, and limited-slip differentials.
I am also looking into getting this to work with the older 323/328 E46s as well!