Difference between
 

What is the difference between Fedora core 4 and red hat 9, besides red hat 9 being older is the gui structured the same??

The main difference is that Fedora Core is not maintained but only supported(in a huge way) by Redhat. After RH9, they split it up in Redhat Enterprise Linux and a community based open source version(=Fedora Core). So you can consider Fedora as the continuation of the free Redhat 9 version, but maintained by the community...

PS: In return, Redhat uses Fedora Core to test all it's new features.

If you are trying to chose between Redhat 9 (RH9) & Fedora Core 4 (FC4) then no-questions-asked, FC4 is the one I would recommend. As far as quality goes they are probably both at about the same level but RH9 is a number of years old now & FC4 is relatively fresh. FC4 also has many advantages over RH9, further developed apps, a newer kernel, better updating facilities, etc. But wait, there's more! Fedora Core 5 is due to be released on March 20th, about 1 week from now, so if I were you I'd wait for FC5 because so far every Fedora release has been significantly better than it's predecessor.

The following is a slightly more in-depth look at the split of Redhat :
After RH9, Redhat, as a community of programmers, decided that their product was good enough to go commercial with, so they became Redhat the company & split their resources, time & effort into 2 separate missions, Redhat Enterprise Linux (the commercial version) & Fedora.
The main & best programmers focused on making Redhat Enterprise Linux as flawless as possible. They only use a kernel version that has been in a stable form long enough for Linus Torvald & the Linux Kernel team to have had 99.9% of it's bugs found, reported & fixed. The same goes for all the apps that make the cut. Only those that have been around long enough that they have been considered stable enough for commercial use, which usually means apps with a version number of 1.0 & above. This has made Redhat Enterprise Linux one of the most stable Linux distro's around. Redhat also wanted to supply full support with Redhat Enterprise Linux so that it could be sold with new PC's mainly to companies, much the same as XP is, but the only real viable way to offer 24hr support & still have your company turn a profit is to have people pay for it.

As for Fedora, they felt that most of their RH9 & earlier audience wouldn't want to pay the bucks simply for the added stability & full support which most long time Linux users don't need anyway. So Fedora was borne. It was kind of created from scratch. A lot of new programmers have been found & a whole new community was set up. The main purpose of creating Fedora was to provide a proving ground for the latest kernels & any new apps that Redhat felt they would like to see introduced into Redhat Enterprise Linux, also, simply making Redhat a commercial venture & asking full-tote-odds for it would mean turning their back on 1000's of loyal Redhat users who are really the ones that drove the development & quality of Redhat to get it to the standard that it is today.

In short, if you want to use Redhat for your servers or what-have-you in a business environment then you would be wise to pay the bucks & get Redhat Enterprise Linux. But if you only want an OS to use on your home PC then Fedora is a great choice. I've been using Redhat since about version 4 & have had every Fedora release & I can safely say that the stability & quality has steadily increased with every release.