So, I assume they'll be downloading the scripts? If so, some thoughts: a] Password protect the site, require a TOS agreement at registration. b] Create a "reader script" which does whatever frontend you require (filling in a TOS form), then reads the script's code from *outside* the web root and outputs it to the browser/whatever.
c] Check $_SESSION vars at the top of each script and redirect to the TOS page if the correct variable hasn't been set (ostensibly by clicking the right boxes on the TOS). HTH,