It gets the second and third line just fine

Proof:

while(<DATA>){
   print;
   if ($_ =~ /^\s*(\d+)\s+(.*?) (\s*)([WS|76])(.*?)\s+(\w+)\s+(.*)\s+(
+.*)/) {
      print "SLOT = $1\n";
      print "Desc = $2\n";
      print "Model = $3\n";
      print "\n";
   }
}
close(FILE);

__DATA__
Mod  Sub-Module                  Model              Serial    
---- --------------------------- ------------------ -----------
  1  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1434RLPY
  3  7600 ES+ DFC XL             7600-ES+3CXL       JAE14520N29
  3  7600 ES+T 20x1GE SFP        76-ES+T-20GQ       JAE145301XM
  5  Policy Feature Card 3       7600-PFC3CXL       JAE14330E6J
  5  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QBE
  6  Policy Feature Card 3       7600-PFC3CXL       JAE14330EAO
  6  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QA8
  7  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QHBR
  8  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QXF9
[download]

Mod  Sub-Module                  Model              Serial
---- --------------------------- ------------------ -----------
  1  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1434RLPY
  3  7600 ES+ DFC XL             7600-ES+3CXL       JAE14520N29
SLOT = 3
Desc =
Model =

  3  7600 ES+T 20x1GE SFP        76-ES+T-20GQ       JAE145301XM
SLOT = 3
Desc =
Model =

  5  Policy Feature Card 3       7600-PFC3CXL       JAE14330E6J
  5  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QBE
  6  Policy Feature Card 3       7600-PFC3CXL       JAE14330EAO
  6  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QA8
  7  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QHBR
  8  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QXF9
[download]

But in your regex I notice a few "funny" parts:

Are you sure you want to capture the whitespaces? I assume you don't.

Are you sure you mean [ and ] here? They signify character classes (much like how \d means [0-9], or "any one digit", [WS] means "any one W or S"), not capture groups. Assuming you meant (WS|76), then do you really want to capture the (WS or 76) separately from whatever follows? My guess is that you meant ((?:WS|76)).*?) here — and I doubt you actually need to specify that this substring begins with the WS or 76, so why not just simplify it to (\S+)?

I'm not sure which parts of the sample data this would match. Did you really intend to have it there?

Modifying your regex according to the above assumptions, and tacking on a $ for good measure, I come up with /^\s*(\d+)\s+(.+?)\s*(\S+)\s+(\w+)$/. Furthermore, I threw in a chomp because I don't want to be bothered with the newlines that are tacked onto each value for $_, so eventually my version of your script looks like this:</c>

while(<DATA>){
   print;
   chomp;
   if ($_ =~ /^\s*(\d+)\s+(.+?)\s*(\S+)\s+(\w+)$/) {
      print "SLOT = $1\n";
      print "Desc = $2\n";
      print "Model = $3\n";
      print "\n";
   }
}
close(FILE);

__DATA__
Mod  Sub-Module                  Model              Serial    
---- --------------------------- ------------------ -----------
  1  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1434RLPY
  3  7600 ES+ DFC XL             7600-ES+3CXL       JAE14520N29
  3  7600 ES+T 20x1GE SFP        76-ES+T-20GQ       JAE145301XM
  5  Policy Feature Card 3       7600-PFC3CXL       JAE14330E6J
  5  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QBE
  6  Policy Feature Card 3       7600-PFC3CXL       JAE14330EAO
  6  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QA8
  7  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QHBR
  8  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QXF9
[download]

Mod  Sub-Module                  Model              Serial
---- --------------------------- ------------------ -----------
  1  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1434RLPY
SLOT = 1
Desc = Distributed Forwarding Card
Model = WS-F6700-DFC3CXL

  3  7600 ES+ DFC XL             7600-ES+3CXL       JAE14520N29
SLOT = 3
Desc = 7600 ES+ DFC XL
Model = 7600-ES+3CXL

  3  7600 ES+T 20x1GE SFP        76-ES+T-20GQ       JAE145301XM
SLOT = 3
Desc = 7600 ES+T 20x1GE SFP
Model = 76-ES+T-20GQ

  5  Policy Feature Card 3       7600-PFC3CXL       JAE14330E6J
SLOT = 5
Desc = Policy Feature Card 3
Model = 7600-PFC3CXL

  5  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QBE
SLOT = 5
Desc = C7600 MSFC4 Daughterboard
Model = 7600-MSFC4

  6  Policy Feature Card 3       7600-PFC3CXL       JAE14330EAO
SLOT = 6
Desc = Policy Feature Card 3
Model = 7600-PFC3CXL

  6  C7600 MSFC4 Daughterboard   7600-MSFC4         JAE14320QA8
SLOT = 6
Desc = C7600 MSFC4 Daughterboard
Model = 7600-MSFC4

  7  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QHBR
SLOT = 7
Desc = Distributed Forwarding Card
Model = WS-F6700-DFC3CXL

  8  Distributed Forwarding Card WS-F6700-DFC3CXL   SAL1433QXF9
SLOT = 8
Desc = Distributed Forwarding Card
Model = WS-F6700-DFC3CXL
[download]

Which sure looks good to me.