I'm using i386 DVD distribution and wonder if it is possible at the time of installation in main memory to install fedora 17 with 4GB virtual disk?

Hmm... let me see if I understand you. You are wanting to create a virtual disk from ram. 4GB. Then you want to copy your DVD to this ram drive, then install? How much total ram to you have? I'm guessing 8GB or more? What happens when you reboot though. Poof stuff gone.

I'm guessing you can't boot to your DVD? I have the same trouble with my laptop. I just took an 8GB thumb drive, and made it bootable and then installed from there. Would that work for you?

If I got lucky and guessed right and you want to easily convert the dvd to a bootable thumb drive, I use opensuse imagewriter. It makes it drag and drop easy. I'm sure there are numerous ways to do this. You may even be able to download an image for your distro already done. ?? Good luck.

Might be able to use a universal usb install. That way the image is compressed.

A full desktop install is like 4.6 gig I think but you may have to double check that. I agree that a normal 8 gig is a good small size.

You could kickstart it to make a more compact install or select in from boot install.