Yes, you can use this HD as an external for your HP Pavillion BUT, to do so you will have to reformt the drive into something that the HP can understand. Currently it is formatted as HFS+, which is kinda like NTFS, but Windows cannot read it without the aid of third party software.
As you know, reformatting the HD will destroy ALL the data currently stored on it.
If you know someone who has a Mac and a DVD burner, you could put the drive into a case (the original plan) connect it to the mac and suck the required data off it. Burn it to a number of DVD's, test them, reformat and go back to the PC.
Alternatively, you could go to a professional who MUST be Mac savvy and get them to extract the data to DVD's.
As a matter of interest, what were the symptoms of the "broke" iMac. I couldn't have been a dead HD, could it?
I have (had) a G3 Imac. It broke, no one quite sure what was wrong. All I wanted was the hard drive, so I removed it. I now would like to put a case on this Mac hard drive (30 Gig G3 Imac Graphite DV) and use it as an external hard drive through a HP Pavillion, WIndows XP. I do not need anything from the hard drive, with the exception of the MP3's and sound files (very important, nearly 12 days of music, plus demo songs of mine. Also, some documents from Word maybe, usually saved in RTF format.) Can I accomplish this? Should I go to a professional?