Can you tell us where you are downoloading the songs and videos from, is it iTunes or somewhere else?
Also can you tell me what type of broadband modem you are using or what type of router?
Can you tell me how your machine works in general, is the machine slow or does it run ok apart from when it is online?
Also can you tell me how much free space you have on your hard drive?
If you open the Mac HDD icoon on the desktop then select your macs hard drive the used and free space will be listed at the bottom of the window.
The first thing to try is a Safe Boot, To do this can you shut the machine down then wait 5 seconds and power it back up.
As soon as you let go of the power button can you press and hold down the SHIFT key and keep it pressed till the machine shows the load wheel below the Apple icon then let go and wait up to 30 minutes for the machine to open to the Safe Boot login.
Login like normal then restart just like normal from the Apple menu and once your machine has rebooted let me know if the machine runs any smoother.
Then can you download a free application called Disk Inventory X from here http://www.derlien.com/ and use it to tell me how much space is taken up on your drive and how much free space you have, This tool can also tell you what is taking up all the space on your drive so let me know.
Has the Safe Boot finished?
If so is it any smooter now?
Did you read my post above about starting by performing the safe boot process?
If not can you you shut the machine down then wait 5 seconds and power it back up.
Just come back to Justanswer.com and it will bring you back here so we can continue, or just bookmark this page and you cna then come back here directly.
keep me posted,
Did the safe boot work and speed things up for you?