Find out your computer's motherboard CPU socket number.
Intel is much more tricky to upgrade than AMD, but its completely do-able so long that the dual-core supports the
socket type.
These are the supported celeron sockets:
Slot 1
Socket 370
Socket 478
LGA 775
Socket M
These are Core 2 Sockets:
BGA479
Socket M
Socket P
LGA 775
BGA956
FCBGA6
LGA 775