This is just a little FYI about what happens when you plug the Dell Streak into a Windows computer.
A pop-up window appears when the Streak is connected to a PC that lets you select what you want the USB port to "do" for the device: charge it, connect via MSC/UMS like a regular flash drive, or connect via MTP so you can sync with Windows Media Player. Contrary to what it says in the window, you can drag-and-drop media and other files to and from the Streak in both modes.
Other than being able to sync with a media player, the only difference you'll see when choosing one connection mode over the other is in My Computer on your PC. In MTP mode, an image of the Streak will appear under "Portable Devices"; in MSC/UMS mode, the regular external storage icon will show up under "Devices with Removable Storage." Clicking on either one does the same thing (displays the microSD card content and lets you add/remove files), so unless you need to sync, it doesn't really matter which one you choose.
You can change the connection mode at any time by tapping the USB icon in the notification bar.