diff -urpN modules/system/memorywarn.js modules/system/memorywarn.js
--- modules/system/memorywarn.js	1970-01-01 01:00:00.000000000 +0100
+++ modules/system/memorywarn.js	2007-12-17 18:50:39.000000000 +0100
@@ -0,0 +1,52 @@
+Drupal.behaviors.memoryWarn = function (context) {
+  $('input.form-checkbox', context).each(function () {
+    $(this).click(function () {
+      var memInfo = Drupal.getMemoryInfo();
+      var memUsage = Drupal.getMemoryUsage(this);
+      if (this.checked) {
+        memInfo[0] += memUsage;
+      } else {
+        memInfo[0] -= memUsage;
+      }
+      memInfo[0] = Math.round(memInfo[0] * Math.pow(10, 2)) / Math.pow(10, 2);
+      // warn
+      if (memInfo[1] - memInfo[0] < 5.0 && this.checked) {
+        if (!confirm(Drupal.t("Activating this module could result in Out of Memory errors.\nDo you really want to continue?"))) {
+          this.checked = false;
+          return;
+        }
+      }
+      Drupal.setMemoryUsage(memInfo);
+    });
+  });
+};
+
+Drupal.getMemoryInfo = function () {
+  var memInfo = Array();
+  var memData = /([\d\.]+)[^\.\d]*([\d\.]+)/.exec($('#meminfo').html());
+  memInfo[0] = parseFloat(memData[1]);
+  memInfo[1] = parseFloat(memData[2]);
+  return memInfo;
+};
+
+Drupal.getMemoryUsage = function (object) {
+  var checkboxes = $('.package input.form-checkbox').get();
+  var thisRow = -1;
+  // search this object
+  for (var i = 0; i < checkboxes.length; ++i) {
+    if (checkboxes[i] == object) {
+      thisRow = i;
+      break;
+    }
+  }
+  // get the tag with the description at the found index
+  var memUsage = $('.package *[@title]').map(function(){ return this.title; }).get(thisRow);
+  if (!memUsage) return 0.0;
+  return parseFloat((/([\d.]+)/.exec(memUsage)[1]));
+};
+
+Drupal.setMemoryUsage = function (memInfo) {
+  var newText = String($('#meminfo').html());
+  newText = newText.replace(/[\d\.]+/, memInfo[0]);
+  $('#meminfo').html(newText);
+};
\ No newline at end of file
diff -urpN modules/system/system.admin.inc modules/system/system.admin.inc
--- modules/system/system.admin.inc	2007-12-17 17:48:06.000000000 +0100
+++ modules/system/system.admin.inc	2007-12-17 18:50:39.000000000 +0100
@@ -599,6 +599,7 @@ function _system_is_incompatible(&$incom
  *   The form array.
  */
 function system_modules($form_state = array()) {
+  drupal_add_js(drupal_get_path('module', 'system') .'/memorywarn.js');
   drupal_rebuild_theme_registry();
   node_types_rebuild();
   menu_rebuild();
@@ -641,6 +642,10 @@ function system_modules($form_state = ar
     $form['name'][$filename] = array('#value' => $file->info['name']);
     $form['version'][$filename] = array('#value' => $file->info['version']);
     $form['description'][$filename] = array('#value' => t($file->info['description']));
+    // the memory setting is optional so we have to check that it's existing
+    if (isset($file->info['memory'])) {
+      $form['memory'][$filename] = array('#value' => $file->info['memory']);
+    }
     $options[$filename] = '';
     // Ensure this module is compatible with this version of core and php.
     if (_system_is_incompatible($incompatible_core, $files, $file) || _system_is_incompatible($incompatible_php, $files, $file)) {
@@ -1750,6 +1755,24 @@ function system_sql() {
 }
 
 /**
+ * Returns information about the memory usage
+ */
+function system_memory_info() {
+  $meminf = array();
+  // get the current memory usage of the PHP parser, transform
+  // it in a Megabyte unit and round it
+  $meminf['in_use'] = round(memory_get_usage() / 1024 / 1024, 2);
+  $meminf['limit']  = floatval(ini_get('memory_limit'));
+  // if there are less than 5 MB of Memory remaining, set the warn CSS class
+  if ($meminf['limit'] - $meminf['in_use'] < 5.0) {
+    $meminf['state'] = 'error';
+  } else {
+    $meminf['state'] = 'status';
+  }
+  return $meminf;
+}
+
+/**
  * Default page callback for batches.
  */
 function system_batch_page() {
@@ -1992,13 +2015,26 @@ function theme_system_modules($form) {
   }
   ksort($packages);
 
-  // Display packages.
   $output = '';
+  // Display memory usage
+  $meminf = system_memory_info();
+  $info = '';
+  if ($meminf['state'] == 'error') {
+    $info = t('Drupals memory usage is too high. Please deactivate some modules or raise your memory limit to prevent Out of Memory errors.');
+  }
+  $output .= '<div id="meminfo" class="messages '. $meminf['state'] .'">'. t('Memory usage: @mem_in_use of @mem_limit MB. @info', array('@mem_in_use' => $meminf['in_use'], '@mem_limit' => $meminf['limit'], '@info' => $info)) .'</div>';
+
+  // Display packages.
   foreach ($packages as $package => $modules) {
     $rows = array();
     foreach ($modules as $key => $module) {
       $row = array();
       $description = drupal_render($form['description'][$key]);
+      $memory_info = '';
+      if (isset($form['memory'][$key])) {
+        $memory_info = t('Estimated memory required: @memory MB', array('@memory' => $form['memory'][$key]['#value']));
+        unset($form['memory'][$key]);
+      }
       if (isset($form['status']['#incompatible_modules_core'][$key])) {
         unset($form['status'][$key]);
         $status = theme('image', 'misc/watchdog-error.png', t('incompatible'), t('Incompatible with this version of Drupal core'));
@@ -2030,7 +2066,7 @@ function theme_system_modules($form) {
       }
 
       $row[] = drupal_render($form['version'][$key]);
-      $row[] = array('data' => $description, 'class' => 'description');
+      $row[] = array('data' => $description, 'class' => 'description', 'title' => $memory_info);
       $rows[] = $row;
     }
     $fieldset = array(