According to HP, that model has either the Intel i810 or i815 video card. I believe those chips were only made for the AGP bus. But, I wouldn't be suprised if HP only gave pci slots for expansion. I used a video card with one of these intel chips a couple of years ago. Worked very well. I don't have the G2 version of realflight, but it seems to me that you should have enough computing power (according to the system requirements) to use the 3d terrains. Do the graphics work, but just run real slow?? Computers are so different, it is hard to tell, but you may be able to try just going into the BIOS and giving the AGP video more memory to work with. AGP chips usually have on-board memory, but also share the main RAM in the pc. Most motherboards have adjustable settings for how much memory is shared. You will probably have to upgrade the video card, but just thought I would give you something to try to see if you could get the results you want.

Good Luck!