themes not updating on local installation of WordPress

I installed WordPress 2.9.2 locally on my Mac for all the various reasons that people do and while the installation itself is fine, I cannot edit any of themes, both the default ones that come with WordPress and the ones I’ve created and uploaded myself. Every time I edit a piece of code anywhere in the theme (be it a .php or .css file), the change is not reflected when the layout is refreshed (I’ve cleared my cache, etc.).

Any ideas why this might be happening? Thanks!