If you are just interested in a fixed number of lines per record you can:

use strict;
use warnings;

my $num      = 1;
my $recLines = 2;

while (!eof DATA) {
    ## Open the file once every iteration
    my $outfile = sprintf("Int_%s.txt", $num);

    print "---> Create file $outfile\n";
    printf("%-1s%-12s%-8s%-4s%-4s%-10s%-33s\n",
        "H", $outfile, "20101221", "1230", $num, $., " ");

    for (1 .. $recLines) {
        last if eof DATA;
        last if ! defined (my $line = <DATA>);

        print $line;
    }
    printf("%-1s%-12s%-8s%-4s%-4s%-10s%-33s\n",
        "T", $outfile, "20101221", "1230", $num, $., " ");
    print "<--- Close file $outfile\n";
    ++$num;
}

__DATA__
1234567|HP|GASS
1234567|TP|GASS
3456789|YU|GASS
3245678|TY|GASS
[download]

Prints:

---> Create file Int_1.txt
HInt_1.txt   2010122112301   0                                        
+  
1234567|HP|GASS
1234567|TP|GASS
TInt_1.txt   2010122112301   2                                        
+  
<--- Close file Int_1.txt
---> Create file Int_2.txt
HInt_2.txt   2010122112302   2                                        
+  
3456789|YU|GASS
3245678|TY|GASS
TInt_2.txt   2010122112302   4                                        
+  
<--- Close file Int_2.txt
[download]

Note that the sample doesn't include the file creation code, but what you had was ok. However you should always use the three parameter version of open and you should use lexical file handles. Your open should look like:

# input handle:
open my $inFile, '<' $source or die "Can't open '$source' $!";

# output handle:
open my $outFile, '>' $target or die "Can't open '$target' $!";
[download]

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