It involves some excel work and data loads...After creating the below object you will need to do something like... say for example you have 2 zipcodes in your spread sheets and 5 accounts in your org.
1. Extract all the Account Id's (all 5)
2. You will need to make another file in such a way that everyzipcode should be associated to every account...  eg: 2 zip codes...(63121 and 94118) and 5 accounts a1,a2,a3,a4,a5 then your file should contain
    Zipcode		AccountId
    63121		a1.Id
    63121		a2.Id
    63121		a3.Id
    63121 		a4.Id
    63121		a5.Id
    94118   		a1.Id
    94118	            a2.Id
    .....			...... till a5.Id
Then Insert into below object.... In this way we can calculate distance between each zipcode and everyaccount... then you can runyour report by putting filter on distance and summarized by zipcode to find all the accounts in particular radius. 
3. After performing all the steps below and inserting the data as mentioned above.. extract Id's of the distance object above and just make a dummy update on the above object on Id's.. and make sure you keep the batch size of maximum 10... and if it doesnt work then make the size as 1... this way it will populate the Distance field on the below object with the distance between zipcode and the associated account.

Let me know if you have any questions.

Step 1: Create a new Custom object called "Distance" (Api name Distance__c) and make Name field as Auto number...

Fields in Distance Object:

Field Name		API Name		Data Type           	
Account		Account__C		Lookup(Account)
Account Address	Account_Address__c	Formula(Text) (Account__r.BillingStreet +" "+Account__r.BillingCity +" "+Account__r.BillingState +" "+ Account__r.BillingCountry +" "+ Account__r.BillingPostalCode)
Completed		Completed__c		checkbox
Distance		Distance__c		Number
Zipcode			Zipcode__c		Text(Max size)

Step 2: Setup->Security Controls-> Remote Site Settings Click new
	Remote Site Name  : Google
	Remote Site URL    : https://maps.googleapis.com
	Active                    : True

Step 3: Create Apex Trigger and Apex Class on Custom object
Apex Class: 

Public class GoogleAPI {
  public static boolean isApexTest = false;  
@future (callout=true)
  public static void find(Id Id, string origin,String destination) {
   
   Integer distance  = 0;
     Distance__c d = [select distance__c from Distance__c where Id=:Id  limit 1];
     String start1= EncodingUtil.urlEncode(origin,'UTF-8'); 
     String destination1= EncodingUtil.urlEncode(destination,'UTF-8');
           
     //http://maps.googleapis.com/maps/api/distancematrix/xml?origins=Vancouver+BC&destinations=San+Francisco&sensor=false

     HttpRequest req = new HttpRequest();
   
     req.setTimeout(12000);
     
     req.setEndpoint('https://maps.googleapis.com/maps/api/distancematrix/xml?origins='+start1+'&destinations='+destination1+'&sensor=false');

     req.setMethod('GET');
        
     Http h = new HTTP();
     
     HttpResponse res;

     // Send the request, and return a response   
     try{
        
         system.debug('Request>>>>> '+req);
         if(!isApexTest)
            res = h.send(req);
         else
             res = new HttpResponse();   
         
         if(res.getStatusCode() == 200)
         {
          system.debug('*******Success********');
    
          Dom.Document doc = res.getBodyDocument();
       
          Dom.XMLNode response = doc.getRootElement();
          
          dom.XmlNode rowNode = response.getChildElement('row',response.getNamespace());
          
           for (Dom.XMLNode c: rowNode.getChildElements()) {
               
               if ('element'.equalsIgnoreCase(c.getName())){
                   
                   for(Dom.XMLNode c1: c.getchildElements()){
                       
                       if ('distance'.equalsIgnoreCase(c1.getName())){
                       
                           for(Dom.XMLNode c2: c1.getchildElements()){
                       
                               if('value'.equalsIgnoreCase(c2.getName())){
                       
                                   system.debug('Distance between two places@@@@>>>'+math.ceil(integer.valueOf(c2.getText())*0.000621371));
                                   d.distance__c = (math.ceil(integer.valueOf(c2.getText())*0.000621371)).intValue();
                                   d.completed__c = true;
                                   update d;
                               }
                           }
                           
                       }
                   }
                   
               }
               
           }
                       
          }else{
   	//do something...
           System.debug('***Failed to make a callout***');   
         }
   
       }Catch(System.CalloutException e){
        //Failed to make a callout   
        System.debug('***Failed to make a callout***');
   
       }   
    }
  }

Apex Trigger: 

trigger distance on Distance__c (after update) {
    for(Distance__c d : trigger.new){
        if(!d.completed__c)
            GoogleAPI.find(d.Id, d.zipCode__c,d.Account_Address__c );
           
    }
}