are you trying to validate a URL or just a hostname? a URL has a LOT of valid non word characters (at least in certain positions... [_-/:@?#+~.] any other?) if your are trying to match just the hostname then this would do (tell me if i forgot something)

unless($URLcheck =~ /[A-Za-z\-\.0-9]+/) {
    #reject this..
}
[download]

Update! i've found this on slashdot, i see a short life for my regexp :-)