Query: Does my Deskpro EN support PCI graphics with DDR??

Hello All,
I have an age old Compaq Deskpro En series (PII, 128MB, 6GB, S3
vision986, 686T3 bios) computer.

I have a couple of queries::
1) I would like to change my existing PCI video card (S3 vision 986)
with a new Radeon based PCI graphics card that has on board DDR ram
and TV / DVI out. Would my Compaq Deskpro support that card??

2) Are there any issues specific to my Deskpro model for changing the
graphics card?

3) Is there any onboard VGA card in my system? How to find if my
system has an onboard video card or whatever and also how to disable
it??

Thank you all for your time.

Regards,
Pisuku.