First off, tell us what results you get from this
hdparm -tT /dev/hda
It might be /dev/hdb or /dev/hdc. The easy to check is with mount and then use whatever is mounted as / or /boot, assuming your using a single harddrive.
If the Timing buffered disk reads are around atleast 30 mb/s then we no atleast its not a disk controller issue.
Then get your swap usage. If its close to being fully used up then maybe its as simple as increasing your swap. FC is supposed to automatically set all this stuff though so I doubt thats it.
Once all of that is out the way, you can try this.
http://initng.thinktux.net
Installation is as simple changing init your kernel parmater to init=/sbin/initng once you have the program installed ofcourse.
If thats not enough, you try this.
www.suspend2.net/
I think its automatically installed with some distros. Atleast Suse has nice convienient little gui for it.
Also you might want consider switching window managers to something a little less resource intensive, like fluxbox. Which loads significantly faster than KDE or Gnome.