did you intentionally avoid using $longip()? :P with it, you can map valid IPv4 addresses onto their integer counterparts, making them much easier to compare. it also implicitly validates them: an integer return value implies a valid IPv4 address. mIRC 7.1 also introduced a new $iptype() identifier which returns 'ipv4' if the input is a valid such address.

careful with /tokenize though: $isipaddress(1...1...1...1) = $true. also, due to using isnum, $isipaddress(+1.-0.+00000002.+3) = $true. making these kinds of things bulletproof is often a pain ;P