Don't know how to fix my iMac/external HDD

I'm guessing the HD is dead, but it won't even boot to DVD. I power it up and it's just a blank screen. It had been slowing down over the past couple of days, and finally this. How much does Apple charge to replace a HDD? I don't want to mess with it.

Now, I've got all my data backed up to an external HD. However, it's formatted for Mac and is unreadable by my Windows 7 machine. I installed MacDrive, but with the HDD connected, it just says "Target disk is corrupted and unreadable." That can't be right, though, as I was just using it perfectly on my iMac getting some last-second data off of it before it crapped the bed.

Any ideas on how I can at least get the data off of the external HDD to my Windows machine? My wife has an older Macbook which will read the external HDD. Is there a way I can access that HDD over my network to copy things to my PC?

Edit:
Well, I've got it so I can use my wife's Macbook to access the HDD and can transfer stuff to my Windows machine. It's godawful slow, though... 40 mins for 5 gb. And there is over a terabyte of information. Is there a quicker way to do this?

Or, is there another way I can just hook up the HDD to the Win 7 machine?