Can someone please give me a straight answer im leaving for Costa Rica in the morning and need my music.
There are many ways to (semi-)automate the process. I'm assuming you don't want to use an app to manage this. (There are dozens. I expect some other answers will suggest some.)
I also assume that you know how to connect to your PC and turn on "USB Storage".
Just copy your music files to your SD card. The music player will find the tracks wherever you have them, but you should probably put them in a "Music" subfolder so that you can find them easily.
It's as simple as that.
You can copy the music to any location on your phone, and the music player will detect the location automatically.
Al has posted how you can transfer your file with a PC and USB cable, if for some reason it doesn't work for you you can install Awesome Drop from the Market and then use Dashwire's awesome drop to transfer the file using internet connection.