I got a strange error when trying install RHEL 6.0 on my VirtualBox: "Probling EDD (end = off to disable)". Although the default Memory is set to 512MB. The problem got fixed when I change the memory to 384MB or just change the....size of installation Windows. Not sure it's a kernel or Memory or...size problem. Hope this help!
+ PS: I got no problem when using VMware 7.0. Although when you choose 384MB of RAM, you just got the basic installation. With 512MB of RAM you will see the graphic one.