These are instructions on how to determine the bootrom version of your iPhone using Windows.

Step One
Connect your iPhone to the computer and put it into DFU mode. If you don’t know how to do this you can find instructions here.

Step Two
Press to launch Control Panel from your Start Menu.

Step Three
Press to select Hardware and Sound from your Control Panel window.

Step Four
Press to select Device Manager from the Hardware and Sound window.

Step Five
Double click to expand the Universal Serial Bus Controllers category

Step Six
Right click the Apple Mobile Device USB Driver item and click the Properties button.

Step Seven
Click to select the Details tab.

Step Eight
Select Device Instance Path from the Properties dropdown.

Step Nine
Scroll to the end of the field to locate your bootrom version. It should look something like [iBoot-359.3]

***If you have an iPhone 3GS, iBoot-359.3 is considered the old bootrom. iBoot-359.3.2 is considered the new bootrom.