Umigumi is a powerful but very dangerous program. It may erase completely your hard disk. It may download unsafe code from the Internet with unpredictable effects. Always backup your hard disk before you use Umigumi. If you are not certain of what may happen with Umigumi, simply click on the OK button now and then click on the Quit button.
Now, a nice word about Umigumi: it can install for you in a few seconds flash memories (ex. Compact Flash, USB key, etc.) with ready made setups created by Open Source / Free software developers and turn your OpenBrick or any PC into a WiFi access point, an ADSL router, an MP3 player, etc.