code:

$strComputer = "."
$count = 0
$crits = 0
$colItems = get-wmiobject -class "Win32_Process" -namespace "root\CIMV2" `
-computername $strComputer | write-output

foreach ($objItem in $colItems) {
      $objItem.WorkingSetSize = $objItemSetSize / 1024
      if ($objItem.WorkingSetSize -gt 25600) {
      write-host  $objItem.Name, $objItem.WorkingSetSize -foregroundcolor "red" -backgroundcolor "black"
      $crits++}
     else {
     write-host  $objItem.Name, $objItem.WorkingSetSize -backgroundcolor "black" -foregroundcolor "yellow"}
     $count++
}
write-host $count " prosesses running " $crits " are using more than 25 MB memory" -backgroundcolor "black" -foregroundcolor "green"

example output:
PS C:\Documents and Settings\USER\Desktop> .\tasklst.ps1
System Idle Process 0
System 0
smss.exe 0
csrss.exe 0
winlogon.exe 0
services.exe 0
lsass.exe 0
ati2evxx.exe 0
svchost.exe 0
svchost.exe 0
svchost.exe 0
ati2evxx.exe 0
StyleXPService.exe 0
svchost.exe 0
svchost.exe 0
spoolsv.exe 0
explorer.exe 0
Dit.exe 0
rundll32.exe 0
avgcc.exe 0
Steam.exe 0
msnmsgr.exe 0
ctfmon.exe 0
avgamsvr.exe 0
avgupsvc.exe 0
avgemc.exe 0
mDNSResponder.exe 0
vmware-authd.exe 0
vmnat.exe 0
vmnetdhcp.exe 0
alg.exe 0
svchost.exe 0
wuauclt.exe 0
usnsvc.exe 0
TRACTION In-Game Radio Player.exe 0
powershell.exe 0
SetPoint.exe 0
KHALMNPR.exe 0
flock.exe 0
notepad.exe 0
wmiprvse.exe 0
calc.exe 0
42  prosesses running  0  are using more than 25 MB memory