I've just spent a few minutes searching via www.google.com/linux
for information about xfx geforce 5600 cards, and I don't find anything which says activex is required. That may just be a windows requirement.
Linux provides the nv driver for nvidia graphics (2d graphics). It's a fairly easy matter to download the nvidia driver (for 3d graphics) from their website and install it (easy is relative: easier on some distros than on others).
My suggestion: before you install, download and burn to cd a few livecd distributions. Power up with the livecd in the drive, and run Linux from cd instead of the hard drive. Find out if your hardware is detected and enabled.