I have local administrator access on my machine but somehow still can't change the screensaver setting. I believe it is being disabled by group policy somehow, is there a way to override this?
You "own" the machine if you have local "Administrator" rights so, yeah, you can.
Mark Russinovich talks about circumventing group policy in this blog post, and just happens to use display settings as an example. Lucky for you, eh?
Basically, remove all access to the registry key where the policy setting you're looking for is set and the policy stops applying (since Explorer can't read the policy setting). This might not work in the general case, but Explorer happily ignores not being able to read its policy settings.
For types of policies that don't apply via registry settings (i.e. policies that use other extension handlers like IE policy, folder redirection, etc) you'll need to employ other means to circumvent the settings client-side.
Before anybody critisizes me for letting a user in on a "secret" way to circumvent their IT department's policies think about how the sysadmins, in this case, shouldn't be granting users local Administrator rights to begin with.