I'm using an Antec Three Hundred Black Steel case with these parts:
Geforce GTX 465
OCZ 4GB RAM
OCZ 600W PSU
1TB 7200 RPM Samsung F3 Spinpoint
would I need extra fans if I'm not going to be OCing my system?
This will be used mostly for work and some gaming here and there.
Run your build and put it under load
If you are getting high temperatures, then buy some fans...