the multiplier is locked internally on all Intel chips, don't even think about changing it, it won't work.
Your processor runs at a default 66.66 mhz bus speed with a 9.5 multiplier.
Your only option is to adjust front side bus speed. It is always best to do it in small increments rather than one big move, run it awhile and see if it's stable.
You will need decent cooling, if a retail processor than additional case fans, bay fans to move hot air out and pull cool air in.
Overclocking has risks, computers won't boot, hard drives get corrupt, etc. Be warned
You also have to factor in the agp and pci bus when overclocking as they are a ratio of the front side bus.
Normal speeds are 33 mhz for pci bus and 66 mhz for agp bus
With your current machine your pci bus is using a 1/2 divider to get the 33 mhz, you agp is using 1/1. If you take it to 100mhz front side bus the pci bus has to be changed to 1/3 and the agp bus has to be changed to 2/3 to be at the correct speed.
Overclock the pci bus to much and data corruption, load failures, etc. Overclock the agp bus too much and the video card will crash, lock up, or just plain fry.
Results from site listed below
Celeron II 633 Results....
Total Entries in Database for Celeron II 633 - 151
Average overclocked speed - 977 Mhz
Most of the above users where running special cooling, either oversized high power heatsink/fan combos or water cooling. Most had to up there vcore voltage to 1.9 or above. I wouldn't take vcore over .2 higher than default, it's just asking for a melt down. Also increaseing the voltage increases the heatload calling for more cooling.
http://www.overclockers.com/ in the cpu database