Hello, 
Just a quick and dirty example using nslookup command: 
#include <Constants.au3>
Local $hostname="autoitscript.com" ;just a hostname example using autoitscript.com
Local $DNSserver="8.8.8.8" ;just an example using Google DNS server (if you want to use default server just remove the ip: Local $DNSserver=""
$GETNORMAL=_NormalLookup($hostname,$DNSserver)
If @error Then
	MsgBox(0,"","Error trying to get ip for " & $hostname)
	Exit
Else
	MsgBox(0,"","Normal Lookup for hostname " & $hostname & " is " & $GETNORMAL)
EndIf
$GETREVERSE=_ReverseLookup($GETNORMAL,$DNSserver)
If @error Then
	MsgBox(0,"","Error trying to get reverse lookup for " & $hostname)
	Exit
Else
	MsgBox(0,"","Reverse Lookup for ip " & $GETNORMAL & " is " & $GETREVERSE)
EndIf
Func _ReverseLookup($fip="127.0.0.1",$fDNSserver="")
	Local $Consigue=Run(@ComSpec & " /c " & 'nslookup -type=PTR ' & $fip & ' ' & $fDNSserver, "", @SW_HIDE,$STDERR_CHILD + $STDOUT_CHILD)
	Local $line
	While 1
		$line &= StdoutRead($Consigue)
		If @error Then ExitLoop
	WEnd
	Local $array=StringRegExp($line,".*name\ =\ (.+)?",3)
	If @error Then
		SetError(1)
	Else
		Return StringStripWS(StringStripCR($array[0]),8)
	EndIf
EndFunc
Func _NormalLookup($fhostname="localhost",$fDNSserver="")
	Local $Consigue=Run(@ComSpec & " /c " & 'nslookup -type=A ' & $fhostname & ' ' & $fDNSserver, "", @SW_HIDE,$STDERR_CHILD + $STDOUT_CHILD)
	Local $line
	While 1
		$line &= StdoutRead($Consigue)
		If @error Then ExitLoop
	WEnd
	Local $array=StringRegExp($line,"(?s)Name:.*Address:\ (.+)",3)
	If @error Then
		SetError(1)
	Else
		Return StringStripWS(StringStripCR($array[0]),8)
	EndIf
EndFunc
Keep in mind what I said, it is quick and really dirty, it will fail if the hostname has more than one ip, etc. so I recommend to take a look to already implemented functions TCPNameToIP and _TCPIpToName (check the examples in AutoIT help). 
Edit: To add example using TCP functions: 
#include <Inet.au3>
Local $hostname=@ComputerName
TCPStartup()
$tcpnametoip=TCPNameToIP($hostname)
$tcpiptoname=_TCPIpToName($tcpnametoip)
MsgBox(64,"Reverse Lookup", "Hostname " & $hostname & " resolves to " & $tcpnametoip & @CRLF & _
"IP " & $tcpnametoip & " reverses to " & $tcpiptoname)
Cheers,