Ah! help!

Basically I am trying to get a PHP script 'script.php' on bill.com (user bill) (/home/bill/public_html/script.php) to be able to write another domain (both on my server) bob.com (user bob) (/home/bob/public_html/imgs)

I added the user bill to the group bob, changed the group of that directory to the bob group, but then the web service doesn't work because it needs the 'nobody' user. so I added the nobody user the to group, still no dice... so I tried the add both users to the nobody group, which doesnt seem secure, and doesnt work..

all this was done with the directory set to 775

can any linux experts give me a tip or two.. ?