The standard threaded rod on the Solidoodle has given some issues with banding. These parts make it simple to change the rod to a finer and more accurate M5 thread.

Parts list:
200mm of M5 threaded rod with at least two matching nuts.
5mm to 5mm flexible coupling (or similar).

Total cost under $10.

Print the three parts with a high infill for strength. Dimensions in mm.

Official Solidoodle Z platform disassembly and assembly guide can be found here: http://vimeo.com/61632393
I didn't find it necessary to unscrew the stepper motor.

Assemble from the bottom up as per picture.

1. Flexible coupling onto stepper motor.
2. 5mm threaded rod into flexible coupling
3. Slide platform over rod. Place base on platform.
4. Place nut on rod, turning down to sit in base. Place top piece over nut and secure to platform and base with original M3 nuts and bolts.
5. Screw second nut down over assembly and secure by snapping nut hugger in place.

Don't forget to update the steps per mm for the Z stepper in the EEPROM settings / firmware!