If you choose to burn an MP3 CD you go by the file size, so the full 439MB will fit. However, many CD players can't play MP3 CDs, which are just data CDs, limiting its ability to be played back at will. On the other hand, WMP, Real Player, etc. burn Audio CDs (like those you purchased), in which case the songs are actually 'converted' to fit the Red Book specifications. This ensures playback will be successful on any CD player, but means the capacity is based on song length, which maxes out at 74 minutes regardless of file size. It's a trade-off you must make based on the device you intend to play the songs back on.
Hope this helps,
My wife asked me to copy 4 audio CDs on just one CD to play it in the car for our dauthers. I copied all 4 in a folder in the hard drive as mp3s. The folder has a size of 439MB and it should fit easily on a 700MB audio CD. Still, both Real Player and WMP tell me that I need 3 CDs for all the songs in the file I created. I don't understand why such a discrepancy. Any of you guys can help me with this issue? Thanks in advance