192.168.1.10 ivanov
192.168.1.11 petrov
192.168.1.12 sidorov
192.168.0.13 kozlov
..........................................

192.168.1.10 pc1 00:11:22:33:44:55
192.168.1.11 pc2 00:1a:2a:3a:4a:5a
192.168.1.12 pc3 00:2a:3a:4a:5a:6a
192.168.1.13 pc4 00:3a:4a:5a:6a:7a
.................................................. ....................

param ($file1,$file2)

$file1 = Get-Content $file1
$file2 = Get-Content $file2

foreach ($i in $file2)
{
foreach ($j in $file1)
{
if ($i.split()[0] -eq $j.split()[0])
{
$i -replace " (\w|\d|\W)* ","`$0$($j.split()[1]) "
}
}
}