Well, you have your share of problems. First of all, I would recommend in the future you post one problem per thread. It is very difficult to help you when the problems are unrelated. With that said, I will do what I can.
KDE can be installed. Red Hat uses rpm files to install packages. You can get the rpm's from the install media, or from online repo's. You have to configure what repos to use with most distros. I havn't used Red Hat since the split with Fedora. So I hope some one will chime in and provide some details.
O.K. so lets have a go at your sound. If your sound was detected on install, ( you indicated it was ) there is a good possibility all you need to do is launch a mixer program, un-mute the sound, or just turn it up. If that doesn't do it, then we need some information.
What sound card, or chip set do you have? To find out, open a konsole and run the command 'lspci' and post the results. That probably will show the sound card hardware. Also post the results of this command, 'lsmod | grep snd' You probably need to be root to get the commands to work. All commands without quotes.
As for Nvidia, I don't have any experience with Nvidia hardware. There are lots of posts on this board. You many want to read a few and see how to get the sofware installed.
To help you out, in windoze the hardware is supported with drivers. In linux, they are called kernel loadable modules, or KLM's for short. There are reasons for this distinction, I'm not sure I understand all the reasons behind the naming. It is also possible to re-compile the kernel to install the modules needed for your hardware. I don't recommend you try that for a while. The short message here is linux is different to windoze. It helps us help you if you use the correct terminology.
Hope this helps.