This 1gHz pentium you are thinking of getting doesn't come with a stock cooler? Depending on how long it's been since you've changed the cooling pasta on your 667mHz (If you ever did that?) You might need to apply some new cooling pasta to the "new" processor/old cooler...
But really, do you think it's worth the effort? I think you will be hard pressed to tell the difference between the 2 CPUs. If i was you, i would look into changing my software instead of hardware, there a many Linux distros out there which have been designed with low speed systems in mind (My old Thinkpad T30 runs just fine with Xubuntu, while Xp with firefox and Openoffice is a sloppy experience), without knowing which OS you are using now (XP? Windows 2000?) my guess is that installing something like this will be much more beneficial than getting a faster (but still ancient) CPU...
