First, connect your phone to your computer and select "Disk Drive" from the charge menu on the Evo.
2nd, browse your SD card on file browser on the computer. Then Create a folder (if not one already) called "music" by right clicking on the white aread and selecting "new" then "folder" then name it "Music"
3rd, open your folder that you save your limewire Mp3's to, then select the mp3 files you want on your phone. right click the files and click COPY
4th navigate back to your SD card "music" folder, right click on the white area and click paste.
This will copy your music from your computer to your sd/music folder. When done, just unplug your device and your music player should scan the card automatically for your new music.
I would also recommend downloading "ASTRO" File browser for your phone. This is done on your phone through the "Market", its free. Astro lets you browse your SD card files while on your phone.