MacBook :: Sudden Drop In Performance After CD Import Failure

My macbook was running at basic, normal speed, nothing too serious for a year-old laptop, but suddenly one day, my performance dropped sharply, to the point where it would take up to ten minutes to attempt to get to a page, and songs would freeze for about a minute about 3 times per song in iTunes. It all started when I attempted to import a CD into iTunes (it was downloaded onto my HD, not imported directly from a CD), and I got the message "attempting to copy to the disk macintosh hd failed. The disk could not be read from or written to." About this time, my computer started acting unusually slow, (the problems mentioned above).

I did some looking into this, and did both suggestions listed here (Disk permission repair, then manual iTunes folder permissions change):
http://discussions.apple.com/message...623410#7623410.
After this my problems were eased for a little bit, I was even able to import the folder I had been unable to import earlier. But I tried then to import the very next CD (it was an 8-CD set), and then I got the same error. Thinking it was possibly a problem with a corrupted/infected file, so I ran a scan through my whole computer (using McAfee), which didn't return any problems. Then, on top of this, my mac suddenly stopped burning CDs, saying that the CD failed because of a "medium write error."