I was really disappointed about the Iphone 3G once when I update the IOS 4.0 . I was waiting to use all the new features in IOS 4.0 a couple of nice features were not active in 3G like home page image settings, battery % indicator, and multitasking. But let me tell you the performance of the phone had really become impressive after updating the IOS to version 4. But I read in many forum that IOS 4.0 was not up to the expectation! really sad to hear that 
So do not worry if you are unhappy with the jailbreak you can use the iPhone1,2_4.0_8A293_Restore.ipsw to restore your phone to 4.0 default mode.
So today I planned to jailbreak my Iphone 3G and I was success in breaking it and get the hidden features working the way I wanted. I was still wondering why did apple disabled the multitasking feature in 3GS!
Files you require to do it?
Itunes 9.2 Download
IOS 4.0 iPhone1,2_4.0_8A293_Restore.ipsw
Jailbreak redsn0w_win_0.9.5b5-4
Use your Itunes to backup to safeguard your data 
1. Download the IOS 4.0 and save that on your desktop
2. Download Redsnow extract and run the redsn0w.exe file
3. Browse the iPhone IOS 4 file (iPhone1,2_4.0_8A293_Restore.ipsw) from the desktop and click on Next
4. You will be then prompted to select the features which you would like to get it enabled.
( Multi tasking, Homescreen Wallpaper, battery percentage and Cydia app installation.)
5. Click Next, it will instruct to you change your phone in to DFU mode to perform the deploy.
In 10 minutes it will load and restart your phone.
That’s it you are good to go!
Enjoy jail breaking.
