Its better to get an aftermarket cooler because the stock cooler just cuts it, and is really loud. Your CPU will also last longer if it runs cooler. Also, if you live in a hot climate, there's less risk of overheating and reduction of clock speed as a result.
On the other hand, if you can't afford it, the stock cooler is acceptable.
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Sony PCV-RX755 (old but still runs great!)
MOBO: ASUS OEM board
CPU: 2 GHz Socket 478 Pentium 4 Northwood
RAM: 2 GB Kingston ValueRAM
GFX: EVGA Geforce 6200 AGP
HDD: Samsung Spinpoint 100 GB ATA-100