Okay your completly off in this PC, yeah for office I would go intel, but on the other hand AMD is cooler and more reliable now, so I guess I would do that.
The motherboard needs to go, DFI or MSI (MSI K8N Neo 2) is a good recomendation
Power supply, thermaltake td-420AD, cheap, reliable, powerful
EDIT: It's the power supply listed above.
Since you want reliable, run your hard drives in RAID 1 or do at least a weekly data backup (or a combo of both)
Having stuff on one hard drive is not a good idea, and having it in the same PC isnt that good of an idea either