The Second Life viewer has a handy built-in feature which allows you to hide your HUDs from your screen. This is only a cosmetic operation, as the HUDs will still be equipped and working as normal.
There are two ways to achieve this. Since Viewer 3, Linden Labs has added a handy dandy shortcut called Show HUD Attachments to the Me menu, which is the first menu at the top (left) of your viewer. You can also use the following keyboard shortcut to achieve this effect:
Alt + Shift + H
I recommend to not use this functionality as a way to hide lots of HUDs. While invisible, these items still require server resources and contribute to lag. Instead, try to detach as many HUDs as possible. Personally I’ve found that the only HUD I never take off is my AO, everything else can be derezzed ’till needed.