http://kb.siteground.com/how_to_redirect_all_visitors_except_your_ip_to_another_site/

*Rewrite Rule to Redirect IPs*
# Allow IP
RewriteCond %{REMOTE_ADDR} !^1\.2\.3\.4 [OR]
# Allow IP Range
RewriteCond %{REMOTE_ADDR} !^2\.3\.4\.
RewriteRule ^(.*)$ http://www.YourURL.com [R=301,L]

*Rewire Rule to redirect IPs for a certain url -- like an admin directory*
RewriteCond %{REMOTE_ADDR} !^ip\.add\.re\.ss
RewriteCond %{REQUEST_URI} /url [NC]
RewriteRule ^(.*)$ / [F,L]

*Allow/Deny Rule with Custom Error URL*
ErrorDocument 403 http://www.YourURL.com
Order deny,allow
Deny from all
# Allow IP
Allow from 1.2.3.4
# Allow IP Range
Allow from 1.2.3.