[iMeeK]

So this site I was planning on defacing told me I wasn't allowed to view /admin. How can I bypass this

[Krypto.]

Well, this is the .htaccess blocking you from entering the page most likely. There are some tutorials on here about how to bypass it, but its not really possible if you haven't already shelled the site. Try to find another vulnerability on the site other than SQL. Hoping the best.

[xkcamd]

Yea smart people will keep any sort of admin page under a local ip or list of ips using .htaccess. Most likely if you got in with SQLi there might be some sort of LFI thing you can do to get a shell on to the site, but I wouldnt know.