Missed this earlier, but people put WAY too much stock into this whole fragmentation issue. It might account for some delay in loading the game and levels within the game, but once those are loaded, fragmentation would be basically a non-issue. Simple fact is, very few programs are limited by disk throughput, and games aren't on that list.
Similar to the idea that a computer slows down the more the HDD fills up. Not true. It doesn't matter if you've used every last byte of space on a drive, as long as the OS doesn't need any additional space for virtual memory, it will run exactly the same as if the HDD were 75% empty. If the drive is full and there's a demand for more virtual memory, you'll know it pretty much immediately as everything will come to a screeching halt.
And while I'm at it, I'll also say that absolutely nothing CCleaner is capable of will do anything at all to resolve this issue. Dafydd had it pretty well pegged right from the beginning. If a game runs reasonably well at one point, but the performance then suddenly degrades, especially factoring in a roughly 7 year old computer and you're looking at heat related issues almost for sure. Adding more RAM to a system that old also wouldn't be a bad idea to help it cope with more modern programs that tend to assume a higher base level than was common when the system was manufactured.
The reason you see these answers offered up a lot of times is because you sometimes run into a computer hypochondriac who will absolutely not be happy until they find SOMETHING wrong with their computer that can be fixed. So you tell them to run some useless task like defragmenting. It takes a couple of hours, so the person is both out of your hair and assumes that there really must have been something wrong if it takes that long to fix. The problem is some percentage of those people will then go running all over the place acting like they're some great computer sage handing down wisdom for the ages about this defragmenting program and there are plenty of people who simply don't know enough to realize the person telling them this is full of it and hasn't the foggiest what they're on about. The two posts that came after dafydd's are prime examples of this in action.
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