You were on the right track. Try this:

   my $numbers="1 1.0 3.547 92.34 343.2234";

   while($numbers =~ /(^|[^.\d])(\d+)/g) {
     print "$2 is an integer\n";
   }
[download]

Which prints out:

   1 is an integer
   1 is an integer
   3 is an integer
   92 is an integer
   343 is an integer
[download]

For the data you give,    /(^| )(\d+)/g    also works fine.
Sorry... no look-ahead.  %-(