The E5200 family of CPU's is based on the Wolfdale core. They have a relatively low FSB freq (200 MHz) and relatively high internal multipliers (starting at X 12.5). That combination means that they tend to overclock like banshees.
Very important - what motherboard?
And if your motherboard has a locked BIOS (no user access to BIOS settings), you may not be able to overclock your CPU.
This is our generic Core2 overclocking guide (based on an Asus Core2 board):http://www.tomshardware.com/forum/259899-29-core-overclocking-guide
Keep your core voltage under 1.45 volts and your load temps under 70 C.