TBH, there's not a massive amount of difference between DVD drives these days, they're pretty much as fast as they're going to get and very similar spec. I suspect that you'll have an
IDE DVD ROM which means something like this:
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will do the job nicely. It might be worth getting your mate to open the case to check as there's a possibility it could be a SATA connection in which case you'd probably want something like this:
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Either way, you're going to be better off in the long run maintaining the PC yourself, because at least you're in control of your own destiny that way. I have been building my own PCs for 15 years and whilst it can be a PITA sometimes, when something does go wrong I can usually get it fixed in 24 hours at most.
I learnt a very valuable lesson with Eclipse and I'm sure you have as well. Don't try to save £20 here and there because in the long run it's just not worth it. I buy from Novatech, Scan and my local PC shop when I need something generic or in a hurry. These shops offer top quality components, a top class service and most importantly, they are well respected by the enthusiast community which means they can't afford to treat people like dirt or they'll lose business very quickly.