The version number stayed at 7720 for me, so this is not the 7740 update that was released to some customers last week.
Internet Sharing is found on the Settings Menu, select Internet Sharing and then slide the switch to the On position to bring up the configuration. The HD7 will have a default device name and password which you can customise easily by just selecting the fields and updating with your own preferences.
Once you have the details set, click Setup and sharing will be enabled and your Broadcast Name will be visible to WiFi devices. Connect as you would any WiFi Hotspot and share in the O2 HSDPA goodness (depending on your area!).
Internet Sharing supports up to 5 connected devices at once, but bear in mind that performance will suffer the more devices you connect.