First make sure you set your activesync to not allow usb connections and set your phone to mass storage in settings/connections. After that turn off your phone. Open umdl and click on Unified File Image. I assume you have the beta rom file on your desktop so click on the desktop button on the left select the file and click open. You'll see that several of the blank fields in umdl now have info in them. Now click on Detect.
Plug in your phone and make sure the power is still off. Once it's plugged in go ahead and power it up, the umdl should detect it and it will instal the firmware. Wait for the blue highlight on the umdl, that will indicate it's complete. Your phone should reboot once it's done if I'm not mistaken. After that your beta rom will be officially installed.
You will use those same steps for 1.0, but instead of clicking on Unified File Image you will instead click on the button labled PDA.
In the side bar at the site where you got the beta rom there should be a link for a guide, I reccommend downloading it because it has the step by step instructions and it also has images to help you along the way. It really helped me out.
