Hi.....I too need a save file but in recent browsing i found that the process is confusing..We have to modify two directories for xp in the local settings folder/app data folder go to microsoft folder where you will see the xlive folder which is your gta4 profile folder which has the specific user id...we have to modify the whole (copy and paste) the folder with the profile no, may be paste there so that we may have 2 profiles(iam not sure about this)...so wat we need 1. save game folder
2. xlive folder from the same user
its worth a try but having a backup is safe.