Disclaimer: As always, this is a guide only and I accept no responsibility for any damage or injury that maybe sustained through following these guidelines. This was on my GS430 Sport, the GS300's are exactly the same, the IS and LS I would expect to be very similar.
Tools I would recommend:
- Trolley Jack
- Axle stands x 2
- 1/2" drive Ratchet handle
- 10mm Socket
- 12mm Socket
- Phillips screwdriver
1. Jack up the front of the car and put on axle stands. To do this job you will need BOTH wheels fully off teh ground, or BOTH fully on the ground. The anti-roll bar will be twisting if you only have one wheel off, and you seriously don't want to undo the bush brackets under those circumstances.
2. You will now see the under tray below the engine compartment. The antiroll bar is behind this so it needs to be removed.
3. There are numerous screws holding the panel in place. Use a 10mm socket to loosen them, and a phillips screwdriver to make the complete removal quicker.
4. Belly pan off
5. The antiroll bar, bush and brackets are now visible (both sides look the same)
6. Use the 12mm socket to undo the two bolts holding the bracket on
7. The bracket coming off and the exposed bush.
8. To remove the bush, they have a big split in them so that they can be opened up and pulled off the bar.
9. The bush off
10. Old and new bush
11. The old and new on top of each other. You can see the lip half way down the hole where the new one has a smaller hole than the old one. Explains why mine were knocking 
12. Reassembly is just the reversal of the steps above.
13. Go for a drive and relish the knock free silence over small lumps and bumps