Celerons are budget processors - the difference between a Celeron and the equivalent Pentium used to be that the Celly had 25% of the cache - it could store less in the ultra-fast cache memory, and had to use slower system RAM more often, killing performance on many kinds of operation. I'm not sure what the difference between the current celly and the P4 is, but the celly will be crippled in gaming performance. Still a decent chip, but you will not see incredibly performance from it.
www.tomshardware.com probably have a comparison that will tell you just how bad it is. My supper is burning as I type, so Ill look it out later.