I understand your skepticism. I suspect the new system's KT266A chipset and going from PC133 ram to DDR has alot to do with the increase in speed.
I also upgraded the Cdrive from a three year old 27 gig, ATA 66, 5400 rpm hard drive to a 40 gig, ATA 100, 7200 rpm unit
Why did I spend the money?
About two weeks ago the old system started to misbehave. At first it would crash the news reader Agent while it was down loading a large number of large files. But it would recover after it had finished the download. Then it started to completely freeze, not respond to alt-clrt-del nor mouse input, while running Agent and required a hard reboot. Then it started to freeze when moving files from one hard drive to another or at seemingly random situations. At about this time rebooting it corrupted the registry and I would have to reinstall most of the drivers and some of the applications. After a hard reboot my Cdrive crashed and I replaced it.
To fix the system I:
1. Updated NIC drivers
This did not fix the problem and the situation got worse.
2. Replaced the RAM
This did not fix the problem and the situation got worse.
3. Replaced the powersupply
I think I screwed the motherboard while doing this because the system did not boot at all.
I needed a working computer for my job so I decided to do a cpu\motherboard upgrade.