evaluate date/time from file - count instances of line 1 week back

ok, not the best title but I'll try & explain.

I want to:

1. log username that logs on to PC

2. log time of login

3. write this info to a file

4. open file, count number of times the same user logged on to PC going back 1 week

5. if count equal or greater than 10, do stuff.

right now I've got this:

$user=[Environment]::UserName
$pcName=[Environment]::MachineName
$time = get-Date
##ModelType Query
$modelType = Get-WmiObject Win32_ComputersystemProduct | Select-Object -Property Version
##Modeltype.version is the one we want

$var1 = $user
$var2 = $pcName
$var3 = $ModelType.Version

##test the variables
$var1
$var2
$var3
$Time

#write to text file - Username and append
$outfile="C:\tmp\LoggedInUsers.txt"
Write-output "Login Time = $Time", "Username = $var1" | out-File $outfile -append 
$LogStats = Get-Content C:\tmp\LoggedInUsers.txt

Example of the content of $logstats:

ogin Time = 01/15/2014 14:46:27
Username = mrt
Login Time = 01/15/2014 14:46:31
Username = mrt
Login Time = 01/15/2014 14:46:35
Username = mrt
Login Time = 01/15/2014 14:46:39
Username = mrt

so it should look for "Username" and grab what's next to the '='

and the same for login time.

then go back 1 week from Today and count username instances.

Any help will be greatly appreciated.

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Kindest regards, Martin