Here is some information about downloading music:

Music Sources:
Limewire - get Limewire Pro http://www.limewire.com/ - Make sure you are connected when you do a search on Limewire.  Search for Audio only - if you don't you might get offensive content.  Order your list of results descending by number of sources (highest number at the top.)  Then make sure that all the sources have around the same file size - this is how you will know you are downloading a song and not an advertisement.  Also - make sure you are downloading from someone with a high speed connection.

Make sure you run a virus scan each time you download music using Limewire.  Although it says that there is no bundled malware with that comes with that software, something is up.  My computer always runs slower after I use Limewire until I run the scan. 

After you are done downloading all the songs you need go to your Windows Media Player.  Go to the library and make sure you are looking at all of your songs.  Press F3 to tell Windows Media Player to search for the new music files you downloaded from Limewire (or whatever other source you use.)  The new files will show up at the bottom of the list.  Make sure you rename your new songs so that the song column contains the name of the song and the artist column contains the name of the artist.  This way when you go to search for the song later you can find it.  You do this by clicking the song title or artist space on the song twice so it becomes editable.

Other Tools:
Mixmeister - tool you can use to measure BPMs in songs (free) - http://www.mixmeister.com/ - go to 'Downloads' > BPM analyzer at the bottom of the page.

Music Ideas:
http://www.promoonly.com/ > 'Music On CD' > 'Radio Series' - lists songs that came out each month by month.  Once you are on the page for a selected month hit 'Print Friendly Details.'  This will give a printable page listing all the details about each song INCLUDING beats per minute.  You will not be able to download from the site, but it may give you ideas on songs you would like to download from other sources.