Given that iOS 4.3.4 for now it can't be jailbroken with redsn0w and if you have an iPad 2, it's not such a good idea to update, here's a very simple method to trick iTunes into thinking you have iOS 4.3.4 installed. If you make this change in the terminal, you will see displayed both in the device and in Windows that you have installed iOS 4.3.4 for your device and iTunes will recognize this and will no longer display the message asking you to update. To make the modification connect your terminal to the computer and open a program with which you can access the system files of the terminal. If you have iFile installed then you can do everything through iFile. After you have access to the system files, navigate to System/Library/CoreServices/SystemVersion.plist and copy this file to your computer. Open it with a text editor (it is preferable to do these steps on Mac) and change the first line from 8J2 to 8K2 and the last line from 4.3.3 to 4.3.4 then reset the device.
After the reset you will see in Settings>General>About that you have iOS 4.3.4 installed and iTunes will recognize the same and will not ask you to install the new version of iOS. By making this change, you ensure that you will not accidentally update to iOS 4.3.4, and I for one recommend you to follow the method.
I also recommend you to save SHSH for iOS 4.3.3 if you haven't done this because Apple is still seeding those SHSHs and you don't know when you'll need them. If you've already jailbroken and chosen for the Cydia application to automatically save SHSH for you, then you should already have SHSH saved for iOS 4.3.3.
