g1smd - 8:55 pm on Jan 17, 2013 (gmt 0)
Rule pattern matches ONLY the path, in this case viewtopic.php and cannot match hostname or parameters.
(.*) matches any number of characters. Use that when ALL requests need to be processed.
"." matches a single character and "*" means "zero or more times".
In this case you need the exact pattern ^viewtopic\.php with the literal period escaped.