[Plugin: Restrict Categories] parse error when activating

I am getting a parse error when trying to activate Restrict Categories plugin.

Parse error: parse error, unexpected T_STRING, expecting T_OLD_FUNCTION or T_FUNCTION or T_VAR or ‘}’ in /var/www/html/wp-content/plugins/restrict-categories/restrict-categories.php on line 30

I am using php 4.3.9. We plan on upgrading to php 5 soon – but wondering if this is supposed to be compatible with php 4.

Using WordPress 3.1.2 with a network (multisite) install.

Any help would be much appreciated, this plugin looks to be exactly what I need.