Sure you can. Here's the info.
I'm copying and pasting because I can't type fast.
If you have on-board integrated graphics and no AGP slot you will have to try to upgrade with a PCI card. If after fitting PCI graphics you have 2 graphics adapters listed in device manager then "disable" the integrated graphics.If you still have problems then probably only a Hard drive re-format and reloading of windows will solve it.
If you are replacing existing graphics- right click on your blank desktop and select properties, settings ,advanced ,adapter ,change ,new driver , display list of drivers ,show all hardware, select standard display types vga adapter, apply and windows will ask you if you want to restart windows, select no and shut down manually so you can replace card then restart later. Then insert your new agp graphics card and restart and refer below for driver installation details, if you are fitting a pci card see instructions following.
Should you experience problems ,start windows in safe mode (f8 when windows starts loading) and remove the display adaptor in the system device manager box and see if the driver is listed in the add/remove programs section in control panel for your old video card, if so remove it. Restart windows and follow driver installation details below.