You don't need to change the distribution you use to get speed, there are several tweaks you can try out before switching.
You can change the desktop environment / window manager you use, the default in redhat is Gnome, try out XFCE (
www.xfce.org), it will be lighter on the RAM usage, and should speed things up considerably.
You can also try disabling services you don't need, using tools like chkconfig and ntsysv (read their manpage by typing "man chkconfig" and so on in a terminal).
Lastly, as Redhat 9.0 is a bit old, you should probably switch to a newer distro anyway. Ubuntu is a good choice and will be faster than Redhat, but it still uses Gnome, but you can switch to anything else if needed.