Ok, you install the emulator on your phone through the Android market, then you will need to download ROMs (games) to your PC. Then connect your Streak, mount as USB drive to transfer files (on the Streak) and drag the rom files onto your SD card (the drive that will appear on your PC). You can put the ROMs wherever you want, personally I made a /roms folder then /gb /megadrive for the different platforms.
ROMs will be either .gbc, .gb, .gba, (game boy etc) most of them are just .bin though,
When you open the emulator on your phone you will be presented with a file browser which will start at your SD card root and you can just navigate to your ROMs.