Need help

I have an old computer that have sdram pc66 .Now my question is can I replace that with pc100 or even use both at the same time? I have a Compaq deskpro 4000. I have look for the answer on the Compaq website but I had no luck. Any idea or suggestions ?

By the way does any one know what the maximum amount of ram this Deskpro can support?

You can probably find the anwers here:
http://www.crucial.com/store/listmodel.asp?cat=RAM&mfr=Compaq&productline=Deskpro&submit=Go

I didn't know the exact 4000 you have.