How can I detach my imac stand from it?

Generally, you cannot. At least not easily. If you buy Apple's VESA mount adapter, it comes with a tool to help with remove the stand (you also need to undo some screws), but it is for the 24-inch iMac only, and it is not meant to be something you do constantly.

There are bags and cases that are specially made to carry an iMac. For example

http://mylugger.com/index.cfm?fuseaction=upgrades.products&subcat_id=1

I have not used any such products.

I have not used one, but since the stand is not made to be removed, they would have to be designed to fit the iMac +as is+. I'm sure you can send an email to the manufacturer (or reseller) to find out how they fit (and get supported) inside the bag.

I did not say it was impossible. 🙂 I just said it was difficult, and not something you want to do regularly. For the 20-inch model, you probably need to open the case up to do it.

Forget it. The 20" iMac was not designed for easy removal of the stand. It takes a lot of disassembly before you can reach the stand screws. If you want to travel with your iMac, get a case that will hold and protect the entire system; removing the stand is not going to be practical.

Regards.