Before you just up and download this random file from Apple's website, note this knowledge base article in which Apple notes that your iPhone/iPod touch will be erased in order to perform the 2.0 install.
"Normally if you choose to update, the iPhone or iPod touch software is updated but your settings and media are not affected. If your device currently has a software version prior to 2.0 (1.x) and you are updating to software version 2.0 or later, all data on your device will be erased in order to perform install the new software. In this case, iTunes will offer to create a one-time media backup of your device depending on what content is on your device and what content is stored in the iTunes Library you are connected to. You should ensure that you have enough free space on your Mac or PC to accommodate a backup that matches the capacity of your iPhone or iPod touch (4 GB, 8 GB, 16 GB, or 32 GB) if you proceed with the this backup," explains Apple.
To install this update, you must download the ipsw file and iTunes 7.7. Open iTunes and clicking the option + clicking the check for update button will prompt iTunes to ask for the ipsw location; once you've done that, iTunes will begin the firmware update.
Auntie TUAW's note: we would recommend you wait for the "official release" of the 2.0 firmware; it's not a good idea to go poking around on Apple's servers and download random files for installs.