How to save files in a build dynamically?

[satyanarayanagv]

hi,
iam using cocoa touch navigation controller application. in that i need to do the following tasks,
1. i need to download an xml.
2. i need to use the xml data on the screen.
if specify the path related to mac. it is working fine. but it wont work if it is really placed in iphone.
can anybody please tell me how to place new files in iphone build.
the code i used is

NSMutableData *receivedData=[[NSMutableData data] retain];
/////// some operation to fill received data
[receivedData writeToFile "sample.xml" atomically:YES];
/// the above sample file is placed in root.
/// but i want to place it in iphone.
/// if i use the below statement..

NSString *appPath=[[NSBundle mainBundle] bundlePath];
appPath=[appPath stringByAppendingString "/sample.xml"];
[receivedData writeToFile:appPath atomically:YES];
/// it return true but unable to find where the file is.. not in "sample.app" also

Thanks