how does one enable hardware acceleration for the video card after the driver is installed? is it done automatically after the driver is installed?

Enabling acceleration is done in the "DRI" (direct rendering) section of your x config file. It _might_ be done while installing the driver, depends on the author of the code for your card. It should be done by the x config tool for your distro. It can be done by manually editing the x config file. The specifics depend on the card and driver used. Have a look at the docs included with the driver (for example the README and INSTALL files) also, the docs in the /Documentation directory of the kernel source might be of help. And of course searching forums and the web.

Is there an easy way to tell if hardware acceleration is enabled?

(I'm running simplyMEPIS 8 on a Dell D600) Specifically to my situation...
1) I notice that videos run smoothly in KMPlayer and my only reason to suspect that hardware acceleration is not being utilized is that the computer heats up quite a bit during video playback (maybe it's using the CPU instead of the graphics card?).
2) I notice that Flash and other videos run poorly in Firefox, using mplayer plug-in and the Shockwave Flash plug-in. Perhaps this is a sign that I am normally utilizing hardware acceleration, but these Firefox plug-ins are not?

Thanks!

Check glxinfo | grep renderer.
If there will be "Software renderer" than hardware acceleration is off.

Thanks, Samotnik. Upon running
/$ glxinfo | grep renderer
I got
OpenGL renderer string: Mesa DRI R200 20060602 AGP 4x x86/MMX/SSE2 TCL

After a bit of googling*, it seems to me that hardware acceleration is enabled, but due to the jittering and slow speed I mentioned earlier, I suppose it's just not working in Firefox plug-ins.

Thanks again!

*if you're a n00b like me and curious what all that output line means, here is the result of my googling:
Mesa 3d is an implementation of the OpenGL graphics standard.
DRI, "The Direct Rendering Infrastructure... is a framework for allowing direct access to graphics hardware under the X Window System in a safe and efficient manner."
R200 is a reference to the type of graphics card in many (most?) Dell D600s. By running /$ lspci, I see that it is a Radeon RV250 (and thus of the R200 family)
20060602 I imagine is the date of the renderer software.
"AGP 4x" is for Accelerated Graphics Port, a standard hardware interface for graphics cards, and the speed, 4x
And then I stopped googling, content that hardware acceleration was enabled.

I just got Debian working properly on my D600.

The 3D framerates were terrible, until I installed a wee firmware package via Synaptic (sorry, I'm at work and my laptop's at home. I don't remember the name of the package I installed). Now the framerates are much better, though still not as good as I'd like them to be, and the models in SuperTuxKart are very much distorted.

But, since I never intended this particular machine for gaming, I'm pretty happy.

The laptop's mainly just a platform for tinkering, so I might give ATI's proprietary drivers a shot.