Images from Mac won't upload

Help! I’ve read all the forum responses so far but can’t figure out how to fix my problem. Every time I try to upload a photo to my blog, no matter how small the image, it says:
“mypic.jpg” has failed to upload due to an error
Unable to create directory /var/www/goc/public/blog/wp-content/uploads/2010/10. Is its parent directory writable by the server?
How can I fix this? I’m a writer – not a tech person. Need some step-by-step help. Has anyone had this problem?? I have a Mac v. 10.6.4 and use Firefox 3.6.10. Please let me know!!