Are you sure you want to allow 0 as the first character? Or three 0's as the first octet? IP addresses don't really lend themselves to regular expressions. If you really want to check for correctness i'd do something like this:

foreach $octet (split /\./, $ipaddr) {
    #
    # check each octet here (numerically, not with
    # a regex!), i've gotta jet
    # or i'd write it myself 
    #
}
[download]

Okay, okay, it ain't briefer, but it will probably enforce something more like an actual IP address.

Then again, if you are just trying to pick out IP addresses in text, you might be alright with your regex... You won't find strings like '304.00.3.999' very often in text files.

Hope this helps,
Mark