This is a difficult question to answer.
Most notebooks have the integrated graphics card (especially business models) though that seems to be changing as more consumers insist on better graphics since they are using them just as they would their desktop.
Even so those darn cards are custom designed and their are hundreds of them out there with only the few specified ones originally designed for your notebook being compatable.
For the ZD8000 they list
64MB ATI Mobility Radeon(TM) X300
128MB ATI Mobility Radeon(TM) X600
256MB ATI Mobility Radeon(TM) X600
I do not know this for an absolute fact but in general when there are options like this then they are seperate socketed boards.
That said if you have the 64MB or a 128MB card I would think that if you were willing to pay the exhorbanant price that HP would charge for a 256MB card that you could upgrade it.
That would be the only scenario I could see for a possible upgrade.
These are not the kind of cards you find at the computer store, or on ebay (unless a machine is being parted out).
In general though due to most notebooks having an integrated card, the limited number of cards the notebook is designed to support (BIOS issues and such, usually only three specific video cards or less), the special non-standard design of all these video cards meaning you must buy the OEM card, and the outrageous price that HP will charge you for that video card
The correct answer is really NO!
If you like a notebook with some growing power stay away from HP, maybe get something like the ASUS that I have been reading about where you get a barebones and construct out of parts you purchase for it.