How to legally bind users to T&C without registration?

Allowing users to access and utilize, even if in limited fashion, your flash gaming website can serve as consideration to support their obligations under contract (i.e., the Terms of Service, or ToS). A user's "registration," what ever that term could mean, would not necessarily be a prerequisite to you being able to enforce your ToS against him.

The larger concern will involve the content of services you are offering over your website (e.g., gaming, as in gambling?) and how you may (i) best limit your liability to users and (ii) ensure you are not running afoul of various state statutory requirements, like Cal. Bus. Prof. Code Section 22575.

Terms of Service and Privacy Policies are certainly not one-size-fits-all instruments; consulting an attorney to review the contracts you are proposing to execute with the anonymous internet population is advisable.