In before flames.
EDIT: Ok, I'm here. Here's whats wrong buddy.
YOU CANNOT OVERCLOCK A PROPRIETARY BOARD/COMPUTER.
Now that said. Your Pentium 4 and 8500GT PCI (notice the lack of a "e"?) are going to stuggle to max out CS:S, so why are you complaining about Crysis?
No offense, but you should get to know your system and compare it to others before you think that a simple FSB increase will magically get crysis to pull 4x AA on Very High.
And no, you're system specs aren't "good". For an average user, maybe, but not an overclocking community that has members running rigs with THOUSANDS of dollars of hardware, dual quad core CPUs, 8GB of RAM, and quad-GPU solutions that I dream of at night. My system can barely be called aqudate.
link if you want to OC your Dell.