Why do you want to partition? If you're going to go with three, I can see having one for a bootable partition, and one for TM so in case you want to start the backup over all you have to do is erase the drive, it takes forever to manually throw out the backups. And then the last for just extra space.
If you don't want a bootable backup two will do. If you're not concerned with erasing the TM backup, you can just use the whole drive, other files can reside just fine on the drive next to the backups.backupdb folder
I just want boot-able partition for TechTool Pro and DiskWarrier and Time Machine partition.
Also, my hard drive in iMac is getting full and I want to keep movies and pictures on new drive.
I don't need a partition for TM you say? Okay.
So should I not partition at all? Make the whole disk bootable? How do I do that what do I choose in Disk Utility. Or make a small bootable partition? Crackers. Just get a larger drive I tell myself, it will all be better!!
You can make make one small bootable partition, and use the rest to hold TM and all the other stuff.
Remember though that the movies and pics can't be backed up to TM if they reside on the TM partition.
But also another thing to consider is that even if you have a separate partition for the movies and pics and back it up to the TM partition, it's not really a backup even though they are in two places, it's still the same drive. If the drive dies, so do all the partitions, the data, and backups. Did I explain that in English?