Are you talking about RAM or hard disk?
Assuming RAM, if the RAM modules are of the right specification and appropriate size, then yes, they can be re-used.
However, there's not a lot of point in adding 128MB to a system with 2GB already installed, especially if the old RAM is slower than the existing - it might even slow the system down.
What you will probably find, however, is that a) the memory from the old PC is not compatible with the new PC and / or b) even if it is, the RAM slots in the new PC are already full - and the old RAM modules are lower capacity.
Best you can hope for is that you have free RAM slots and the old RAM is compatible.
SD