Although I'm not saying the Celeron processor is the fastest processor in the world, the newer ones will certainly fit the Pentium II class or better. I've got an 6-7 year old 366 mhz Celeron that is still running fine. (At one time, the computer ran about 10 - 12 hours daily, although now it's only used once or twice a week.) My one year old XP HOME computer is running a 2.6 GHZ Celeron and it also is doing a great job with no hiccups (about 6-8 hours per day currently)...Recognize that these aren't gaming machines and are only used for internet work, school work, and general home use..
I also have a few customers that run their machines 12 hours a day for years...Most have had no problems...Some have overclocked their Celerons and made fairly decent game machines out of some of the older stuff.
So, although I wouldn't recommend the Celeron as a high end processor for the elite customer, I have seen them work fine for the purpose you intend...As "glb613" suggested, make sure that the operating system on the computer is compatible with the program. That's more important than the specific processor type...
Hope this helps.
Grif