well, those Corsairs are good power supplies, but they're certainly a bit pricey. You can get a good power supply in that wattage range for far less, if you catch a good sale.
Newegg currently has the OCZ StealthXStream 600watt power supply on sale for $54 w/ free shipping(it was recently on sale for $40, but you missed that deal, unfortunately). That's a high quality power supply selling for a great price. In the review of that power supply at HardwareSecrets.com, they found that that power supply could actually put out 728watts of power, despite being labeled for 600watts. That power supply would probably be fine for your computer.
Do you know any of the specs of your computer? Like, do you know what kind of CPU it was? Dual core, single core, quad core, tri core? Intel or AMD? Core2Duo? Also, would you have any idea what graphics card you had? Do you have one or two graphics cards? One thing you can certainly check is how many hard drives and optical drives the computer has. If you open it up you can also find out what graphics card(s) you have. Any specs that you know would help us estimate just how much power your computer requires. Even if you were to just tell us how old the computer is, how many CD drives and hard drives it has, and if you have one or two(or integrated) graphics cards, we could come up with a pretty good estimate.
You may be just fine going with the Antec Earthwatts 430watt PSU that tuksonrider mentioned above, as that is a very good power supply, but I'd have to know the specs before I'd know if that power supply could handle your computer.
One other resourse that you can use is the Eggxpert Tiered Power Supply List. This lists out many power supplies, divided into tiers depending on their quality. So, if you're looking at power supplies to buy, you can check them out on the list to quickly see if they are any good.